You don't need PCIe 3 yet, not for a long time... Even a 6990 is well shy of pushing PCIe 2.
On Bulldozer, AMD got it very wrong with that, they concentrated it on high frequency apps and multi-tasking, 3D modeling, multi-sample x264 encoding, rendering, Raw number crunching power...... the like.
Its not a bad chip as many Intel fanboys would have you believe, if you look at CRAY's latest supercomputer you will find it full of Bulldozer cores, they think its powerful and it is.
Bulldozer has a lot of internal power (Raw processor power) Sandy Bridge has a lot of external power (fast threading lanes ect..) The former is computation power, the later is x86 application power
Its just not set up for everyday mainstream apps, as a result its a rather large step back from its (now very old) Phenom II predecessor [for everyday use] don't forget Thenom is pre the Apple inspired (copied) Intel ' i ' prefix CPU's.
They have publicly acknowledged its no good for what most want it for, and promised to get back and track with its next CPU (PD: 2012) and more with the one after that (SR: 2013 / 2014)
Actualy you know what? If you were to put Intel's threading lanes on Bulldozers cores you would have an absolute monster!