For OCing id go with OCZ, i belive they have looser timings allowing yout to get a higher OC.
If your OCing consider watercooling as you CPU will get pretty hot (go with the 3500+)
as for the graphis cards im not too sure on the Gigabyte version, i recomend BFG techs version as it is already OCed (but that up to you)
For the Mobo go for MSI, since it supports SLI that board will stay with you for a long while.
PSU a Antec 420W should suffice
Theres my opinion, enjoy

to 1nterger- i think that the CPU is just as important as a graphics card, but thats proby just me