I was reading the specs of ati radeon 5770 ddr5, and I noticed it's 128 bit (Please correct me if I am wrong). Does it mean it has no added benefit compared to cards that have 256 bit but are ddr3? (I am only asking you to consider ddr3/ddr5 aspect)
This is a trade between bus size and memory clock
A 448 bit bus on the GT260 with GDDR3. (Bandwidth 111.9 GiB/s) Is as adequate as. A 256 bit bus on a HD4870 with GDDR5. (Bandwidth 115.2 GiB/s)
in reality they are not directly comparable by memory type/bus, for solid compassion you should check out the reviews of this GPU.
There are many other factors that impact the speed of a GPU such as memory latency and on GPU cache that they dont advertize that are just as important.