The issue I'm running into is I can't find any AM3+ boards with a PCI-E 3.0 slot.
That's because there aren't
Not a huge deal, though (at least not yet). No single current 3.0 card (except for possibly the GTX 690) is truly
bottlenecked by 2.0, currently. It's a 1% difference, at most.
3.0 really matters more for super high end SLI/Crossfire setups (we're talking something like 2 or more 680's or two or more 7970's).
Don't worry about it.