New imac, as in just released (the ones with the 2 tone and horrid 16-bit lcd's?) I run a lab of 32 of the previous gen ones (brand new intels pre 2 tone) and 5.1-1.4 ran great and 6.0 is running smooth as well. Limited ram hurts, but It's great for dvcpro Hd and less projects. I cant see the new ones being any worse other than their lack luster displays.
semi side note, I've experienced less stability based help issues than the 2.6 macpro's In a different lab. This may be do to the simpler class based work done in here vs the more free form work on your own projects in the mac pro lab. Not sure