The top of the range iMac can beat pretty well every MP made, but the iMac will come with Mountain Lion and FCP 7 is not supported.
It will work of course, but there may be some items that don't function as expected and the situation will get worse as operating systems are upgraded.
With new computers, FCP X is the only recommended (Apple) app.
[How did this question get to FCPX category?]
Thanks for your response.
I think I'll back up my current Mac Pro and upgrade to Mountain Lion to see how FCP7 performs with the new OS. I keep searching for results online to see comparision from th Mac 27" i7 to my Mac Pro and get benchmarks numbers which are confusing. I can't find any side by side comparisions. Also, my computer is not list in any results.