Which graphics card to choose for my new rig?

I just built a new system, and I'm wondering which graphics card to choose from. Currently I have a BFG GeForce GTX 260 OC Maxcore 55 896 MB. But I can still return it for a refund since it hasn't passed 30 days yet. The other two cards I'm looking at are:

HIS H487QT1GP Radeon HD 4870 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported IceQ 4+ Turbo Video Card

SAPPHIRE TOXIC Radeon HD 4870 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card

I've read a lot on these forums and others comparing GTX 260 to Radeon HD 4870 and they both are very competitive. But I want some of you guys advice on which one. Right now I'm leaning on returning the GTX 260 and getting the Sapphire.

My rig:

AMD Phenom II x4 945 3.0 Ghz AM3 Quad Core.
AsRock A780GMH/128M
Corsair 4gb DDR2-PC8500 (might upgrade to 8gb)
Seagate 300gb Barracuda 7200rpm (old hd, doesn't even have 3.0 sata)
Ultra X-finity ult-xf500
Samsung 23" 2333SW LCD Monitor (1920x1080)

Thanks!

I suppose that's true...however since I'll be gaming at 1920x1080, the benchmarking sites that compared both suggests that the 1gb of memory from the 4870 would help.

I like both the HIS and Sapphire, but I read that HIS most likely runs cooler but is noisier, while Sapphire runs a bit warmer but the noise is quieter. In that case I'll go with the Sapphire most likely, if I do indeed change...