Hey, Bill, first off, Welcome to the Forum!
I have two C-9s, and a 9mm H.P. Comp. and as far as the accuracy goes, they are all pretty much alike-- on somes days, one of them will kick butt, then on other days, one of the other ones will! (Couldn't be the shooter, right? Nah---) The Comp is a little more confortable to shoot, because of the extra weight, but I really can't tell much difference in recoil, among the three. It would be an expensive venture to have the longer barrel installed, (don't think H.P even does that--), it would be much cheaper just to get a new Comp, but I don't know if H.P. even offers them, anymore-- (Suggest checking their Web Site--)
There are some issues with the Comp, that I have encountered, for instance the Compensator has a tendency to work loose after a while, and you have to retighten it on the barrel, with the Allan wrench they provide, (it is secured by a hollow head Cap Screw).
I haven't found the Comp to be that much of an advantage over the regular C-9, so I would suggest you pick up the used C-9, if it is a good deal, (I'd estimate around $125. should be about right, price wise, for a used one)
Let us know how you made out!
Cheers,
Fred (Honcho).