It seems to me (and I'm quite willing to be enlightened if I'm wrong) that all "race" style cans will add a little to the top end (if well developed), trading for a little loss low down. Back in the day, it was accepted that on carbed bikes (there were very few fuel injection ones around - I'm talking 70s/80s) you replaced the stock air filter and upjetted to suit to get the best from any race exhaust. I have had a gen 1 with Akrapovich can and had it Dynojetted, which worked fairly well. However, it seems to me that if you want to be truly happy with a gen 1 with a race can, Ivanising is the only way to go. Any reason you're not? (Seems to me the cost is very reasonable considering the improvement gained - less than my new can on it's own).