I drive my Martin Logan SL3s with an Audio Research Ref 110, and before that a VT 100. Martin Logan speakers work really well with tube amps. But they can sound a bit closed in with out enough power. At one point I had a VT 200 in my system. The SL3s opened up a bit more but not enough for me to justify doubling the number of power tubes. The Ref 110 was a huge improvement over my VT 100.
I know, I have heard how powerful the Ref 75 is. Still if it were me I would opt for the Ref 150. If possible though I would like to hear both amps with the Montis.
The whole Audio Research Ref line of amps is about to be replaced with new SE versions this month. it should be easy to find a good deal on either amp right now.