Hopefully John McNair will pick up on this with some comments. He talks about that in his Red Dog video on "How To Play the 3-string CBG" training video. (Which is an excellent video.)
i think it depend on what tuning you would like to use. i tune A E A using a wound 36 and 26 with a plain 18, and i utilize a 24 3/4 inch scale. using these gauges with your 23 inch scale id be willing to bet when you first tune up the strings will feel best in a B F# B tuning.
that being said i should say that i prefer power chords and dont mess with open major or minor chord tunings
Must you always use strings 5, 4 and 3 (regular guitar strings) to string a CBG, GDg. Is it possible to use strings of different gauges? (Problem is that I bought the wrong strings. They are acoustic medium .026 wound, .017 plain and .013 plain).
32 (wound) 24 (wound) and 16 would be ok for GDg, the problem is that each string has its own tension range in which it can be tuned, go outside of this and it will be either too taut or too loose. Stay roughly around the standard gauges and you wont go far wrong.
I use the above Ernie Ball Slinkys and add a 13 for a 'B' on a four string guitar. (-: