The centering device on the Schwartz chassis (panhard bar, right?) should keep the rear end stable and therefore limit side to side movement - but you still get just a little. Next up is any sidewall flex. I'm not sure how much but as Craig and Don mentioned, cycle the suspension one side up / other down on each side without the shocks / springs connected and see if there is any rub. Bear in mind, your shock compresses only so far which will limit the ability of the tire to go into the wheel well and rub. If no rub, your existing clearance and the extra 1/4" lip roll should do you fine.