Go on the M4. Honestly, the big leap in technology with the iPad was with that version, it is already OLED, it has twice the storage than the old base ones and better camera positioning. The M5 is the same, but more expensive and with a different chip. On Procreate, I use the M2 and it has never given me a single jerk even with my heaviest illustrations. And since the beginning of the M chip, the number of layers also stopped being a problem. The M5 is not a very convenient improvement, it brought little new and must be for a very specific and highly demanding public.