Difference in Demands on Amps

All things being equal, will a Magnepan 20.1 or 20.7 present a more challenging 'load' to your mono-block amps? How does one really quantify that difference if any?
The Magnepan are a pretty stable 4 ohm load.
"Challenging' speakers have wild swings down under 2 ohms.. Magnepan is not one of those.
So basically all you need is an amp with a good capacity to handle 4 ohm loads.
Lots of amperage at 4 ohms and great sound is what is wanted.
I cannot imagine anyone able to differentiate 20.1 20.7 based on how it interacts with an amp..
The only real difference between the two speakers is upgrade, and no biamp.
The new 20.7 is NOT going to be able to be biamped if that floats your boat.. stick to the 20.1

As for amp recommendations: Brystom 7B SST2 or Bryston 28B-SST2
PAss amps...
My question didn't come out quite right; what I meant to ask, is there a difference between the load that a 20.1 or 20.7 would put on a set of amps vs. a pair of Magnepan 3.6's? Are the 20's a significantly more demanding load than 3.6's?
I think there was a thread about a year ago from someone who was having trouble driving the 20.1's with the Cary 500's. If I recall correctly, it was pointed out that the 20.1's had a pretty significant impedance dip to about 2 ohms that you don't have with the 3.6's.
I'd not want to speculate on the 20.7's. The crossovers are different. I'd want to see the impedance curve.
Is it possible to get the impedance curves for the 20.1's and 3.6's?