I really like the speed & performance of W7U x64 build 7057 on my system but....
Yea, there's always a BUT...
There's no problem with Windows 7 Ultimate x64 at all & I really love this OS.

It's extremely fast for one (much faster than x86 on "MY" system's HW) & has better security as well, (here's where the but comes in) but unfortunately all my games are not compatible with it!!! RRRR
They either won't run at all or, there will be video problems with the screen flashing & lines running through it!
Every single program I wanted to install on this has worked perfectly with the exception of games so the only drawback I see with running x64 is not being able to play all my games that I want to on it.
I really wish game developers would start making all their games x64 compatible so that I could run this full time as my everyday OS, but the way things are now if I want to play all my games I have to run x86...
Too bad because I really like the speed, having it able to use 1.28 Terabytes of RAM or more
& having more data processed per clock cycle with better system security running a 64-bit system.
Btw PPM, this build 7057 x64 installed flawlessly in 12 minutes flat doing a clean installation!!!