Funny, I've been actually waiting on the GP6C to add a GP6 to my collection.
I want adjustable sights, the FO front and the extended release for any competition shooting I'm going to do with it, but that's just me.
As for 5" Barrels, I'll be bringing in some GP6-Cs configured that way, but my opinion on the barrels that stick out of the front of the guns (like those franken-glock26s that get imported to Canada, etc.) is that they're butt-ugly. The only reason for the long barrelled GP6s is to get a little more powder burn out of a load, so I expect that only hard-core IPSC Shooters will want them.