3/4 drop is perfect with the stock tires. they will tuck just slightly but not so much that you will rub at every turn. Any lower than that and you will need smaller tires. Don't forget to run drop shocks and keep that tall tire from slamming into the inner fenderwells also. I had a 3/4 on stock tires for well over a year without any problems.
A buddy of mine is running on stock wheels and he's got a 4/6 drop on his truck. The front tires rub the fender during a sharp turns. I did a 3/4 drop on my truck and didn't have any problems with tire clearance.