Honestly, its not looking so good for the last half of June on the Upper A unless it rains. I would consider 500 on the Silverton gauge the minimum for the Upper. Maybe you could go a little lower, but you are definitely going for the scenery at that point.
As for Rockwood, it can be run at pretty much any level, but I definitely would not drive several hours to run it at low water. It is more of an after-work desperation run at low flows, plus it involves about 2.5 miles of hiking for the same amount of boating. Regarding difficulty and levels (Tall Timbers gauge), I would say:
300-800 is Class III
800-2000 is Class IV
2000+ is Class V
Basically, don't bother unless it rains, but if you do come down and want a guide, PM me.