Pass Labs comparison

I am considering a Pass Labs amp to power my Martin Logan Summits (Summits have internal amp for base). Currently using Rogue M-150 amp. Currently on Agon there is a Pass Labs 350.5 for $6,000, a 250.5 for $3,500 and a 150.5 for $1,900. Are there any differences between these amps other than the power? Do you think the improvement generated by the additional power justifies the incremental cost? If so what kind of improvement can one expect? Thanks for your thoughts.