I also replaced my Viper with one of the BMC filters. Far better built and probably more effective due to the design although I didnt get before and after dynos. Bargain at £180 and doing business with Edge Mororsport is always a pleasure.
I have a better suggestion for you.
General concensus in the UK, and a lot of us are running vipers, is that the filter available from Edge Motorsport is slightly better. It's also cheaper! It's a big carbon fibre heatshield job with a massive intake pipe.
UK Price is £180+shipping, as opposed to £230-£250+shipping for the pipercross...