If it's now tuned CFAD, it'd probably easily convert to tenor banjo tuning without any change in strings -- CGAD. The suggestion of GDAE (mandolin -- or octave mandolin -- tuning) is just a 5th higher, and will break your strings if your try it (or sound tubby if you tune down to G from C).

Tune it as it works, don't worry about others' opinions.

Bob