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I've currently got dual GTX-280s in my system which supports triple SLI.

Am I better off getting a 3rd GTX-280 and going triple SLI, or using that 3rd video card as a PHYSX processor instead?

If i decide to go the Physx route, does it matter how powerful the GPU is -i.e. does it make sense to drop some cash on another GTX-XXX card vs picking up a 9600GT or 9800GT on the cheap?

EDIT

Machine is a c2d E8500 running at 4.5ghz, 1200watt PSU in an Antec 1200 case.

Yes, i have a motherboard that supports 3 dual slot video cards. Yes it supports triple SLI. Yes i have plenty of cooling. Yes i have plenty of power. Yes everything else is up to spec and is about as fast as i can manage without going Core I7.

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Side note. I just built a Core i7 box for a friend. Now THAT is a fast machine, even with a relatively cheap graphics card in it (9600GTX? I think it was?). –  Brian Knoblauch Jul 31 '09 at 11:25

3 Answers 3

up vote 7 down vote accepted

For going multi-graphics cards, you need to ascertain these things,

  • Does your motherboard support 3 graphics cards?
    • I think each would be x16
    • given your question & PSU detail, I guess you have a good SLI capable board
    • SLI PSU ref
  • Will your power supply unit take the three cards?
    • this is in terms of wattage and connectors
    • I get the feeling that @1200W, you probably have the connectors too, but worth checking
  • Once you get these things sorted out, the next important angle is the thermal one
    • Do you think you have enough cooling and circulation to handle three heat producing elements kept close to each other?
  • Do you have a multi-monitor setup? or, a high resolution (beyond 1600 horizontal) display?
    • Most of the configurations are not worth unless you have all that visual real estate
    • look at the SLI FAQ on multi monitor setup to figure out your display setup
  • Will you be utilizing all this effort with the applications you use?
    • Are the games you play capable of using all the hardware that you plan (look at the game specs and reviews)

I put up some references in an earlier answer to
Is it possible to run two separate video cards? yesterday.


Update: 3-Way SLI Gets PhysX Debut with Cryostasis and references within.

Legit Bottom Line: A dedicated NVIDIA PhysX card improves performance across the board and a pair of GeForce GTX 280 video cards in SLI with a dedicated PhysX card performs better than a set of GeForce GTX 280 in 3-way SLI!

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Perhaps you misunderstood the question. I am very clear as to what hardware i have (triple SLI motherboard) and what I can run (plenty of power plugs). I am comparing the benefits of adding a 3rd card for triple SLI vs adding a 3rd card for dedicated physx. –  NoCarrier Jul 31 '09 at 7:27

What resolution are you running at? From my experience two 280's will be able to run just about anything on a 30 inch monitor at 2560x1600. Getting a third one would really be overkill if you aren't noticing a problem running some games.

From your setup it looks like you've got a killer rig. If you're thinking of buying high end cards right now I'd say wait until the next flagship cards get released. NVIDIA should have one out towards the end of 2009 or early 2010 and ATI perhaps a bit sooner. Those cards will (possibly?) support DX11 also, something worth noting.

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First off, do you have sufficient power and cooling? Because you're building something serious here.

Furthermore, I wonder what the rest of your system looks like. Since it might be that your third card, regardless of the physics, wouldn't add more performance, because it's not the bottleneck. So please update your post!

From a review by Guru3D I'd say that getting a third GTX 280 would be the best improvement:

Alright, the conclusion really doesn't need to be very long. Money wise high-end SLI and 3-way SLI doesn't make much sense, and it never will. It's bragging rights, and only for very few of you with a 30" monitor actually a wish. See, the GeForce GTX 280 by itself already is a power house.

So as much as I'd like to validate the existence of setups like this, common sense always kicks back in and says: dude .. performance versus money wise you better do something else with your money. And that's the cold harsh truth. This setup as presented today doesn't make much sense when you relate it to the core cash you need to drop.

But hey .. then there are a couple of Guru's out there who will go for these bragging rights, who do want to play their games at the most extreme resolutions with the best AA modes, and these kind of consumers .. might find this a valid purchase.

Now I'm a hardware freak, so certainly .. I won't hold a grudge against you man. In fact, you get my two thumbs up. Because the fact remains that when you factor the money out, the SLI setup as tested today is just an awful frickin lot of fun. I mean playing Call of Duty 4 at 2560x1600 with 4xAA and every possible image quality setting set to the highest possible setting returns an average framerate of nearing 80 with SLI; that will make you laugh a little giggly. Once firing 3-way SLI and to play the game at the same setting at near 110 FPS .. you'll giggle again, yet in a weird girlish gay kind of way, it surely is fun folks. No doubt about it.

So, allow me again to revert to something I mentioned in the introduction. GeForce GTX 280 SLI is much like Pamela Anderson's SLI boobs .. grand, maybe too big, certainly a nice pair to look at .. but surely very expensive. The same goes for Triple SLI which honestly doesn't make sense money wise, but yeah .. it does scale well and we were finally able to Play Crysis in Very high detail, which is just sick to see ... it's that much fun.


Upgrading it with a 9800 would make your system as good as it's weakest link: so either buy a third GTX 280 or don't buy anything. But you also have to consider if it's actually worth it? Since the performance gain you're aiming for will only be noticable at very high resolutions.

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would the 9800 be a weak link if it was dedicated only to Physx duty? –  NoCarrier Jul 31 '09 at 7:29
    
Well Id suspect other parts will be a weaker link before you need any third card, but else yes I think so –  Ivo Flipse Jul 31 '09 at 10:35
    
I haven't seen any games that really tax PhysX ever since it moved over to nVidia. With a single 8800GT 512MB, I can pull a solid 50fps @ 1680x1050 in the old test maps for UT3. A 9800 will work fine. –  Andrew Scagnelli Jul 31 '09 at 12:41
    
The question would also be: will the 9800 only be used for Physx or also interfere with graphics? –  Ivo Flipse Jul 31 '09 at 13:20

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