I used to watch these monsters in the European Rallycross when they were banned from the Rallying. Racing with RS200s, 6R4s, T16s, R5 T2s and Integrales was totally awesome.
I can't remember the exact power figures, a lot depended on the size of the turbo and tune for each particular set up, but the figures were certainly in the 600-800hp range, so the quoted 770hp would be comparable. It doesn't sound quite as wild (no huge flames on the over-run, etc.) but from the way that car is launching out of the corners it is certainly performing!