[Rottweiler]

I have AR uppers with 1 in 7 and 1 in 8 twist. They do fine with 77 grain match bullets. They will outshoot me. Your 1 in 9 would probably be at it's limits with 70 grainers. Best advice I can give there is is try a few.

How many rounds has that upper seen? I'd say about 350.00 would be a fair price unless it's seen over 1000 rounds, then start lowering the price.

As long as the parts are milspec(rare to find some that aren't) any upper should fit any lower EXCEPT colt They use a different sized front pin which requires either an offset pin or a reverse offset pin depending on which part is colt and which one isn't.

Wiggle? are you talking about play between upper and lower? Don't matter. LOTS of discussion has been over this and been proven that play between these two parts has nothing to do with accuracy. The guys who make the "accuwedge" or whatever it is called (a little piece of rubber meant to hold them together tightly) are the firearm equivalent of a snake oil salesman.