A guitar is one place I'd stick with the 1/4" connector. When I do my signature double back flip with a twist I'd raather have the cable come out of the guitar then have the cable come out of the connector. The main place I used to use RG58 was a long run to a phono pre.
Oh, well in that case maybe you should be considering a wireless setup. You could still use a BNC connector on the guitar end of the cable that goes to the transmitter. I remember seeing some sort of magnetic quick-silent-disconnect plug assembly that was designed with the acrobatic guitarist in mind, as a safeguard against getting strangled. I can't remember who makes it, or if anyone ever trusted it to use on stage.
As for me, I'm too old to do a double back flit with a twist. And I play an unplugged guitar so I won't forget to unplug it when I walk off stage.
It can be very confusing ordering the correct cable, BNC connector and crimp die so all fit. I think it took at least three tries beofre I got the right stuff. I have cable, connectors and crimp die for RG59. I think I gave up before I had the right stuff for RG6.
Those tools can get expensive. The best way to get it right is to call a distributor like Arrow who sells a lot of that stuff, tell them what kind of cable you want to use, and they'll sell you the right tools.
Is there some guitar myth about RG-6? RG-6 has lower high frequency loss than RG-59 but you probably don't play too many notes up around 50 MHz even when doing a double back flip. Both the center conductor and insulation are thicker in RG-6 than in RG-59, but the capacitance per foot is darn near identical for the two, and that's what matters most to guitar pickups. But RG-6 is less flexible than RG-59 and might be a nuisance on stage if you move around much. Though maybe you can work up an act where you kick your legs out and spin around a standing piece of the cable. ;)