Vista Ultimate x64; still buggy in SP1?

So I've heard alot of discussion about how Vista x64 has buggy/bad driver support and is generally less usable than x86; is this still the case?* I've been on Vista x86 since SP1 was in beta (and on and off since 4074 )... But I have 4GB extra memory I could stick in this beast if I could trust it.

The hardware is all shiny and newish, so I figure there should be drivers available; and I'd love to run this beyotch on 8GB.* Currently I have 4GB installed but my massive array of hardware memory addresses limits my "physical memory available to windows" to 2.5GB.

Also, I have 2GB XMS2 and the rest is Patriot 800MHz. Obviously, this resulted in a lower winbench (as I call them) after the "upgrade" to 4GB.* I do, however, tend to create a great demand for memory utilization.* Does anyone have tips on DIMM placement order (or BIOS settings that don't involve overclocking cuz I'm paranoid), or do I have to buy more XMS2?