In std form 9.5 is around the max I believe, not because it exposes the oil gallery ( well at least not on the r33 ). Its more due to coil bind and length of the spring on the intake side. If you cut the spring seat a little deeper and run the right dual springs ( with a more open winding ) you can run up to 10mm or more with no coil bind. Talk to LukeVL from Tighe Cams, he has done it and knows all about it.