At what point will I need a new alternator?

I have a 2005 Equinox right now, currently It is just running 2 12"s @ 4ohm, 500w rms. I may rewire down to 2ohm / 900w rms and I would like to add a mids and highs amp that would run somewhere around 300-400w rms. Is that still low enough to run on a stock alt?