BTW: Great thread, I'm rebuilding a used 88T engine I bought, and thanks to this thread I will go with 3mm. The compression numbers where 95, 95 and the engine has 4 years on the rebuild.

I bettter refresh the block b4 installing my Microtech.

 

Overall there is less sealing on 3mm's than 2, check the mazda spec itself the min spec jumped by 5 psi when they shifted from 3 to 2mm seals..
Alot of its dependent on who machines the rotors, how they do it, and the end result. My old 3mm motor, had milling done that was s-shaped , and offset to one side of the rotor, needless to say not only was the compression lower than it should be, but it would have given each rotor a slightly different compression ratio.
Stacking a 3mm rotor on a 2mm rotor, reveals that the a little bit of the vertical wall support of the seal groove is reduced, thus giving the seal more leverage to move back and forth in the groove, its not much only about .005 to .006 of step difference, but it might have something to do with why a set of 3mm rotors I have with only around 20,000 km's on them has more Vee'ing of the groove than all the other high mileage 2mm rotor I have laying around here, it looks like the wear is alot faster on 3mm than 2mm, which could be due to the hardening being removed from the rotor groove, along with the added leverage, I know the lube and running history on the 3mm rotors, nothing adverse was ever done to them operational wise, can't say the same for the 2mms that still look good though..
Something else to think of is that thermal expansion is a function of the coefficient of expansion times the dimension of the part..max

 

Do the 3mm Atkiins seals use 1 or 2 springs? I see that they have a short and long spring.

 

those of you who have had theirs milled who did it and how good did they do.