My 6600 runs just fine at 3.6ghz. I still havent gotten it Orthos stable because i really dont want to crank the volts up until my apartment starts staying under 70F. I've been really debating on lapping my TRUE and cpu though because cores 0 and 3 are almost always 5-10C higher than 1 and 2 at load.
Lapping all depends on how messed up your cpu heatshield and hsf base are. It's definately a YMMV situation. I have seen people drop as much as 10C on load by lapping, but both of their items were far from flat to begin with.