I don’t have a Saturn myself, but as far as I can gather from some googling, Saturn can have two dot clocks (NTSC); ~6.712 MHz or ~7.159 MHz.
With 263 lines and 59.8Hz (?) refresh that would translate to 426.7 dots/line or 455.2 dots/line.
In both cases, the exact dots/line can probably vary slightly from console to console, because I’ve seen lots of different figures of what the vertical refresh of a NTSC Saturn actually is (anything from 59.5 up to exact 60 (neither of which is probably correct)).
427 is given on the optimal timings wiki page, and I’ve seen users report success with it also, but maybe in your case 426 is better?
Also don’t forget to tweak sampling phase.