my suggestion about getting an *86 frame, would be to fine someone who has one and ask if you could shoot it for a couple of minutes. personally I am more comfortable with a 45* frame than an 86* frame. that is all personal preference, and it's something you should be sure about before dumping money into.
the only barrel, that i know of, i can use on my CCM backs is my CCM tip. (I don't know about the stiffi switch) the whole underboring i find is a personal preference also. i went through the whole finding the smallest barrel kits or backs. and me personally noticed i broke more paint, than if i was just sizing the ball so that the majority wouldn't roll out, or just use one of my old barrels that has a big bore. the only thing i saw improved with underboring was efficiency. other than that i find the length, porting, underboring, overboring, and even the color of the barrel is really a personal preference that makes someone comfortable.
so find out what makes you comfortable playing and go with that. I wouldn't spend my money on what makes someone else play comfortable.