I have an early 2011 MBP with the i7 processor and it works great...for higher end stuff also have an iMac 21.5" with the high-end i7 I special ordered last fall. That machine is terrific...ordered 16 GB ram from OWC at the same time and as soon as I setup the iMac, swaped out the ram for 16 GB...quit a machine. Also have three of OWCs 2 TB external hard drives for Time Machine backups and cloned copies of the internal drives and extra storage space.
So, the iMac is a powerhouse, the only one you can change the memory in, though, is the 27" for the latest models.
$1800 for that 2.8 4 core, $620 for the 3.33 6 core plus owc 4x8GB RAM (there is 48GB RAM option for work with lots of large files), and then do the storage stuff = "sweet spot" and performance is excellent. upgrade the gpu later too if when you want. andno worry about heat and cooling, unlike the imac and laptops.