I was running a Q6600 (stock speed), 8gb of 800mhz ram, 10k rpm Raptor, HD4870X2 video. Vista 64-Bit, Home Premium.

I upgraded to i7 920 (stock speed), 12gb of 1600mhz ram, new motherboard obviously (Asus P6T), other components the same.

Initially the computer place put Vista 32-bit on the system.
Outside of cities, even only able to use 2gb of ram, epic flight was much smoother.
The system had a heart attack, when I 5-box hearthed to Dalaran.

Since getting the 64-bit version of Vista back on the system, its smooth anywhere.
I run with every option at the minimum.
Except Spell Effects and View Distance at maximum on one toon.
Without Crusader Aura on the lead toon, I cannot break follow on epic flyers in mid-air.

Not sure on your pricing.
I live in Canada, so we're overcharged and overtaxed on pretty much every product.