The way you want to do it is wait for a stat to be a multiple of 15 away from being capped (485, 470, 455, etc.). Then you use however many Grade 3 feeds you need to cap it. Capping stats early does not waste the stat-gains naturally gotten at Rank Up. It instead forces the stat-gains onto the uncapped stats. Then once you get to Rank 50, you can use the rest of the training on the dump stats (Cunning/Acceleration).

I also don't know that much about how a Super Sprint/Choco Cure III build works. I tend to prefer Choco Cure III/Speedy Cure III builds which have very different stat priorities...