^ what he said. I noticed a gain going from a cat mani to a 4/2/1, but have since ran a saxsport, piper, toyosport, kam system, supersprint, standard and a 1.1 midpipe with a sportex and though the noise is totally different with every system i didn't notice any difference in power.
Though going from the toyosport to 1.1 midpipe and sportex i think it felt quicker midrange. but thats more likely down to the diameter of the pipe, the toyosport is like a turbo system.