Well I would switch over to AMD 64. Your processor is 32-bit. I would recommend getting a 64-bit AMD processor, though that would require getting a new motherboard.
However if you want to stick to Intel, just give me more information on your processor and I'll tell you if it is out of date (or somebody will on this forum as I need to get to bed).
The change from FX5900XT to 6800GT is an excellent choice.
Also always go with BFG by far. You get a lifetime warranty and they are confident in their products, which are of very high quality.