I was in the same situation as you when I was shopping around for a new computer. I knew that the system that I was buying peaked in every aspect. However, I did not want my new system to suffer sluggish read/write speeds. Intel has a newer technology called SRT (Smart Response Technology) which will allocate a SSD drive to cache data from your Primary setup.
My current configuration is:
1 x SATA3 128GB SSD (Read/Write Speeds of 550MB/s)
2 x 1TB 7200RPM Hard Drives in RAID 0
I am getting right about 525MB/s constant speeds on boot, running applications, managing documents, etc. The SSD is acting as a cache for my RAID0 hard drives. I get the space of platters and the speed of SSD.
If you look at even more current motherboards, some of them have a 20GB SSD built onto them for SRT SSD Caching.
In short, I would pick up a Sata3 SSD. Down the road if you're looking to upgrade your system, get one that supports SRT technology and use that SSD as your cache. If you happen to get one with more than 64GB (limit of SRT is 20GB to 64GB of usable SSD space) then you can partition the rest as a separate drive letter. I'll do this and put Photoshop caching on this spare partition.