Evil - if you are looking at the relative merits of different surfaces, there really isn't a need to subtract it out. Whether it goes from 1.2 to 1.1 or .4 to .3, you would still see you had a 0.1 improvement :)

Regarding mounting pressure - if you use bolts with springs and teflon washers between the springs and the bolt head on 4 corners, then you can control the mounting pressure consistency with a good torque wrench or a good machinist's ruler (spring compression height).

Oh, superscript without HTML? Just use ^ to indicate a superscript, or in the case of the degree symbol, leave it out, since most would know if they see 20C it is degrees.