The iMac 2011 with ssd and i7 wasn't the fastest mac it was the mac with the fastest processor speed @3.4GHz, it also has the better sandy bridge processor but it is only a quad core, while the fastest mac pro processor runs @3.33Ghz but that is a 6 core processor unfortunately that is the older westmere, but still a beast with 6 cores.
The imac did very well in single core tasks but can't really compete with multicore/multithreaded tasks when it has to compete with a mac pro that has 6-8-12 cores.
For the type of work you do the more cores the better. So the fastest mac for you is the Mac Pro 12 core 3.06, but best bang for the buck for you would be the Mac Pro 12 core 2.4.
Just my 2 cents.
Hope it helps.