Your ring lands will be fine as long as it doesn't knock. You are using 108 so it's all in the timing, don't get greedy. I've run 22 psi, up to 24 psi all day long on the track with stock pistons on an L motor. 30 psi +(gauge only goes to 30) on the 7M with stock cast pistons. I think turbo will be limiting you unless you, especially if it's a standard turbine wheel. Were did the Supra 550's come from? Only MKIV's had them and they are side feed.