There is no harm in going with a 1500 for the M60. Recognize though that the 1500 can, if you turn up the receiver gain enough, totally incinerate your M60. That is not the case with the M5. I don't know about the M60HPv4. The limitation there may be the crossover board.
Before you do anything, I urge you to write to Andrew. Ask him what the rated average and peak power is for M60HPv4. If the rated is at least 400W, I strongly urge you to set aside any dreams of owning ALFRs and going to ADA-1500-2 and M60HPv4.
If you decide you must keep the ALFR option open, ask Andrew what your ADA roadmap possibilities are so that you don't strand your investment.
