If it can still be had for a reasonable price with the exchange rate what it is, I would go for the 1gb version of the 4870. What resolution do you game on? It might not make a big difference < 1920x1200 or so.
I just paid for my computer about 2 weeks ago(before big price increase)
and I got for about 1500 with tax and shipping included.
a x38 motherboard
4gb of ddr3 memory
a 4870 x2
a 750gb HD
water cooling(swiftech, dtek, thermochill)
lian li full tower aluminum, ocz 700w.
I actually wasn't effect by the price increase as much as you might think because I bought alot of stuff used in canada. Go buy used and you will be surprised at what you can get, I also did alot of ebay too.