It would save you a step if you ended up wanting to downgrade from 5.1.0 to 4.1.0 (instead of 3.0.0). However, it's going to be the same amount of time regardless of whether you do the 4.1.0 part now or later, and it's unlikely you're ever going to want to be on 4.1.0. I would upgrade from 3.0.0 to 5.1.0 following the guide, and I would worry about downgrading to 4.1.0 only in the unlikely event that there's a reason to be on 4.1.0 over 3.0.0.
3.0.0 might get an untethered coldboot exploit someday, and it's nearly impossible on 4.1.0.