Sasha 2 is a 92dB efficient speaker and while it does dip to 2 ohms it certainly does not need nor would benefit from 1200w of power. It is true that power reserve is important but there is a threshold point of "rational reserve" and an "overkill". Wilson speakers do just fine with tube amps at fractions of power of a monster solid state amp. A stable amplifier that is able to comfortably double down with a robust power supply and overhead power reserve is needed to preserve the dynamic contrast and keep the soundstage from collapsing and sound from getting confused and congested. An MC452 is certainly capable of just that.
Going to monoblocks will yield somewhat of an improvement but considering the MC452 is a great amp to begin with, quad balanced, stable and well mannered, it will not be anything "revolutionary" in change.
The MC601s could be a neat upgrade as will the MC1.2KW but it is certainly not required.
On the other hand, if you just have to have the monoblocks, whatever the better deal is would be the way to go, either choice is a good one.
I would be more inclined to put some money into a better/different DAC since THAT will bring about a much bigger change than the difference between the amps.