Levelling Joists

[rothbard]

I am about to put subfloor in.  I used the crawlspace design with 2x12 20' long joists (select structural).  Curious if anyone here did any levelling techniques on their joists.  I discovered after I already finished framing the floor that the crowning and warps in such long joists can lead to quite significant different from one to the next.  I think since I used SS lumber I can get away with planing them down quite a bit if needed (up to 3/4" or so), but also curious if anyone has just scabbed segments of smaller lumber on the sides to level the tops or shimmed them.

This is my first time working with subflooring.  But I have no interior load bearing walls.  Honestly don't care if it's not level, just curious just how bad I can get away with on uneven levelness of joist tops with 3/4" plywood.