Ask the majority of RSi owners and they'll go with me on the Janspeed, theres not much to compare really, the Ashley system is the only other system i know that has its own manifold, its a close second to the Janspeed, but the quality of the ashley systems has been pretty poor

Other systems like magnex etc use the original RSi manifold and downpipe which although better than the standard XR3 manfold its still restrictive.

Its not just about bhp, its about allowing the engine to run smoother and better with a more freeflowing exhaust, also your looking for good quality, something that'll last and not rot out after a year or so, the Janspeed has these qualities