Actually the difference from 35 watts to 100 watts is far less than
that from 5 to 35 watts. In fact the difference from 35 watts to 100
watts is really just discernable. To make a real noticable difference
the power level has to go up by four times. Five to 35 is seven times.

A 2x455 amp will work great. They are called 225's now, because that's
how watts of DC input they use. It's a marketing ploy. Each MRF455 is
good for 60 watts max times a push/pull pair is 120 watts max RMS.
Expect OK audio on AM at 30 to 35 watts of dead key with a properly
biased box. Stay away from Class C (competition box or modulator) units.