Probably boils down to budget more than anything, but i've heard of

300+bhp 1.6 cvh RSTs (Tims grey one)
320+bhp 1.9cvh RSTs (Jamie Goings / Ollies)
250-500bhp (Sunnys old spec engine?) Zetec RSTs

Anything around there has got to be on the cards, but then you probably have to outlay quite a lot of cash to get there.