| If you're looking at a pre-packaged 6-string set, you can pretty much guarantee it's not only playable, but somebody, somewhere has decided it's ideal for some purpose.
If you're looking at buying single strings and making your own custom-guage set, why? Are you not happy with what's out there? I wouldn't think a .035 string would be unplayable as a C string, though it's at the thick end of the range. I've seen C strings as small as .018 (half the thickness), and these will surely sound VERY different.
I usually use a .030 C string. |