Probably free floating the barrel more than you think is necessary will help more than it will hurt. The plastic Remington stocks that I have had were not stiff at all and when shot, the barrel would tap the stock (or the stock would tap the barrel) contributing to some pretty big, unpredictable groups.
On a wood or fiberglass stock, I used to check for a free floating barrel by sliding a dollar bill between the barrel and stock. If it didn't touch it was good. You need much more room with a plastic stock. I like to think of it as space, between the barrel and stock, that you can check with a flashlight or lantern.
