The new iMacs with Retina

The new iMacs with Retina Display look pretty nice.  But all of the iMacs are capable.

I'm using a 27" iMac from 2011, works great with FCPX (I don't have an Adobe subscription).  When I bought it I upgraded the processor to Intel i7 and internal SSD.  So I expect it will meet my editing needs for several more years.

Go for SSD or Fusion internal drive, the regular HDDs take too long to boot and load programs.

Regardless of iMac choice, your satisfaction when editing long-form videos is going to depend upon the speed of external Thunderbolt RAID drives.  I'm using a DROBO 5D but there are faster solutions you could consider.