|"PCIe x16 1.x = 250 MB/sec|
PCIe x16 2.x = 500 MB/sec
PCIe x16 3.0 = 1000MB/sec"
Those are the x1 transfer rates, not x16. PCIe x16 2.0 can transfer 8GB/sec (or 16GB/sec, if you transfer data both ways at the same time--and you can, since PCIe is a full duplex bidirectional bus unlike PCI and AGP).
"I was considering a buildset based on AMD Phenom II X2 570 (yet to be released) versus a build based on Intel Pentium G6960,"
The X2 570 is faster than the Pentium, but what you should really be considering is the Athlon II X4. :)
Super PIII | Unlocked ES Tualatin @ 1.8GHz (150x12, 1.65v, 512K L2)
2GB PC2700 | 500GB | Radeon x1950Pro | Apollo Pro 266T | Win 7 Pro