How much "headroom" does a BPS need?

I'm considering getting a balanced power supply (bps) and would like to know how much headroom the bps needs in everyday usage. My entire system typically draws about an average of 200 watts with occasional peaks of 400 watts if I'm cranking some bass heavy stuff. I donlt anticipate geting any new gear or using the bps in a HT system.

Would a 1000watt bps be sufficient to use or would a larger one be preferable?