Another member & I went chasing down the specs and benchmarks just last week on this. The 680MX in the iMac is specialized just for the iMac. The 780m is "mainstream". It gets about 2% more performance in benchmarks, has the same # of cuda cores and everything. It's virtually the same card. The only chance a new iMac would have a better card is if Apple gets a specialized card again which isn't out of the question. They surprised everyone with the 680MX & I'd wager they'd do it again for the new iMac as the 780M just isn't that much of a spec bump.The 780m may find its way into a revised iMac down the line.