I have a MacPro that's a couple years old, and I'm looking the upgrade the Radeon X1900 that's currently inside. However I've stepped off the video card carousel many years ago and have no idea what's hot, what's powerful, and what's a good buy. Are my upgrade options basically between the: ATI Radeon HD 2600 XT - $129 NVIDIA GeForce 8800 GT - $279 ATI Radeon HD 4870 - $349 ? It seems that the last two cards are only available if I have a PCIe 2.0. I *think* I only have plain ol' PCIe. (It's a 2x2.66 GHz Dual-Core Xeon) If this is indeed the case, am I limited to the ATI 2600 XT? Is this a decent step up from my X1900?