Well, the amp you are using does not appear to be a slouch by any means. Either old or new amp should do fine with those speakers. And room is not big.
I'm thinking you will hear a difference between the two, but perhaps not a huge one on the grand scale of things.
Any tonality, particularly midrange presentation, soundstage, imaging and detail differences noted in particular should be interesting.
I'm guessing McCormack midrange a tad warmer and Icepower midrange more liquid and neutral. Just a guess though based on what I've read about McCormack amp sound in general.
And then there is always the more intangible things like fatigue factor, involvement, etc.
It'll be a fair fight between a very good lean and mean upstart modern amp leveraging a lot of new technology versus a solid but aged veteran. AN interesting bout for sure.
Power bills probably lower with the new amp I'll bet.
P, I'm interested to hear about your findings as you get them. Specs and technology never tell the whole story.
I moved from a 120 w/ch or so Musical Fidelity A3CR stereo amp to Bel Canto 500 w/ch monoblocks, also Icepower (not latest version though). The difference was huge, night/day in most every regard. Also considered Wyreds.
Based on amp specs, I don't think the difference will be as big in your case, but there coudl still be a major difference in that Class D and Class A/B are two way different beasts by design.