we got a 6bhp mid range oncrease from the viper alone, and with teh exhaust and chip (which took us about 3 weeks!) we got about 12bhp more than std.
you might get more, i dunno, ave air temps were about 37 deg C....so HOT
and get NH to do the chip, ours is not appropriate for the UK climate, you will most probably run lean with our setup.