I have a pair of MC 611s, and for the first time in many, many years, I find no need to upgrade (I am rarely satisfied with anything!). However, as sunshdw stated, the move to MC 611 will be slightly incremental with better of everything though. A move to the MC 1.25KW should be much improved over the MC 462 and 611s.
Alternatives would be to run the Luxman M10Xs as monoblocks. I did compare the sound of the M10x stereo to the MC611s. The 611s produced better mid-bass and bass, while the Luxman bested the MACs from midrange upward. But, a pair of Luxmans will run $40K while the MC611s are $16K. I can only imagine what the bass response of the MC 1.25KW would be. I would think that this amp would be the sweet spot of all mentioned here.
Also, the best value/performance would be a pair of Rotel Michi M8s. Enough power to supply your neighborhood! The sound of the McIntosh products and Luxman is sweeter, though, in my opinion.
Lastly, don't rule out the contributions that a good preamp will make in addition to the amps!!