I still do not think it is worth it. Might as well sli/tri sli 285's. Way too much overkill IMO. By the time you'll want sli/tri sli with 295's there may be the 300 line coming and you may want to look into that instead. But i may be mistaken, wait for more feeback.
You also need a good heatsink if you want to overclock the CPU.
If i was you, especially with such a budget, i'd get one (or two) 285's and put the rest of the money you'd save for good watercooling.
edit : oh and don't buy vista. just download the Windows 7 RC 64 bit.