23 or 18 spline?

we ran 23 spline for yearss, had the 3.09 ist gear, in a race car,, 5.57 gears, 340, duster, only prob was, broke a few gears at times, as they were old, we put lots of runs on it, it was proshifted, gear set. ran a 1400 # clutch, then went to a soft loc style. with 1400 # ran a series 300 organic disc. just food for thought.