I believe Miko once said that 1mm = 0.7 compression points. The DE gasket, if I'm not mistaken, is 1.1mm standard???. So, if you used a 0.5mm head gasket the difference would only be 0.6mm. This would equate to a compression bump of 0.42 points, (9.5:1 to appx. 9.92:1). Not much at all.