The cvecs are great pipes. Most people don't take the time or dislike the fact that they have to adjust the baffle to their particular engine. I like them, it can really bring the best out of your engine. If you serious about making it faster then you need to ditch the stock engine. I think your money would be better spent. Then you could always get the cvec later.
But, that's just my 2.5 cents worth of opinion.