Just an advise, don't remove material form the edges, but only the central area. Leave the first ~8mm intact. I once measured the material thickness to be around 7mm. 0.5mm reduction is usually considered very safe. On the other hand I wouldn't touch the original CR of 8.3:1 unless going for over 20psi pressures. IMO people go low comp far too early just because it sounds good in the spec.