The CTRL+Z slowdown, for me, only happened with Max9, and you can get around that by using proper DX9 shaders rather than the ones that come with Max.
Max 8 had no slowdown and neither does Max 2008, afaik, and everything's running as smooth and nice as ever.
The only other thing I can offer to this thread is that your textures are probably all low res in the viewport because you haven't maxed out the texture settings in the viewport properties. It's the first thing I change when I install from scratch, and my textures are always as sharp as possible:
Max>Customise>Preferences>Viewports>Configure Driver: Check both "Match Bitmap Size As Closely As Possible" boxes
