I agree, that's the way I've been doing it. I would add one extra step, make a copy of your 5.x MAS90 directory as soon as you apply the PU so if your migration blows up (and subsequently takes your system files south with it) you can just restore that from backup. Otherwise you end up uninstalling and reinstalled.
Word of warning, though: I have now done about 5 MAS 200 SQL to Sage 100 Premium upgrades and in each one I have found very unusual, and tricky to resolve, issues that (surprise) were not written up by Sage.