Best system for single video card

Hello,

Well I allready got a 570 gtx EVGA, full tower haf case, a dvd drive,hard drive, a heatsink that fits all current sockets, creative sound card audigy blaster, 1920x1080 23" led monitor, keyboard,mouse....Im just missing the obvious:

-Processor
-Motherboard
-Memory ram

And about the psu I don't know if I should get a new one...the one I got is an OCZ stealth x stream 700 watts PSU 85% efficient(supposed to be). It has 72 amps and I have been using it daily for 2 years and every day it's working around 10 hours...should I get another one?

The PC I wan't will be 99% dedicated for PC Gaming(the rest 1% will be to use internet, word,excel and such...no video encoding).

My options would be:

Processor:

1) Phenom II X4 970 (im not overclocking and an AMD build would be much cheaper).
2) Core i5 760(not sure about this one since it would be more $$$).
3) Wait for Sandy Bridge(But prices might scare me).
4) Wait for bulldozer(looks too far away...I need the pc before mid January).

Motherboard:

No idea, USB3 and sata III would be nice for future upgrades but I can't find for myself the best mobo with a single PCI-E lane for the 570 gtx...I'm not into sli...I'm the type of guy that when a better videocard comes out and it's in my range I just sell the one I have and get the new one.


Memory:

I believe I would be fine with a generic(since im not overclocking ATM) DDR3 1333Mhz dual channel...but since it's dual channel it needs to be in pairs like 2-4-8gb ram right?



So yeah. TLDR: A PC that the CPU usage never(or almost never) reaches 100%, that the ram never reaches 100% either...I love having X amount of IE windows while I play and have Ventrilo and hear music.... a PC made for gaming.

Also my 570 gtx is fluctuating all the time, sometimes it gives me 20 fps, sometimes it gives me 60 and other times it gives me 180. I believe it's relationed with CPU bottleneck(ATM core 2 duo E8400 @ 3.00 Ghz) and maybe the PSU could be a problem....let's say I purchase the recommendation I get here, and if the videocard still has problems then I will RMA it and get another one.

THANKS for reading, and Happy New Year