I just got a Marshall Mosfet Lead 100 and that thing when slaved for power is awesome with my RM4! I just got it in a set up a few different situations with it and by running it through the effects loop it is just great! You can pick them up cheap too. It sounds ok by itself but with the RM4 up front it really has the punch that has been lacking with the peavey 50/50. I thought I would share in case anyone is wondering. I had a MosValve as well. This kills them both. It reminds me of the tone of my RM100!