Your going off Peak Power ratings. They are a irrelevant, NEVER look at them. You are asking if downgrading to a 800w amp from a 900w amp is good, I wouldn't do it... Now that amplifier Chevy posted would be a small upgrade... Wait have you even mentioned what amplifier you are currently using?
Judgeing by the rest of this post.. im pretty sure his 900w amp is a 450rms amp...