So sanding the bottom of the hsf will make it do better?
Definitely. The TRUE has probably one of the worst stock bases out there. This is a good and a bad thing. The good thing is that it is already one of the best if not THE best performing HSFs money can buy, it gains more from lapping that any other heatsink and pulls further ahead.
Here is a pic of a stock TRUE's base:
As you can see, it is convex. Only a small portion of the surface is making contact with the CPU, this makes for very inefficient heat transfer.
When the base is lapped, the whole of the base should be making contact with the CPU's IHS. The heat transfer is much more efficient and performance is improved drastically.
Here's PokerDegenerate's thread about lapping, it should give you a lot more info: http://www.computerforums.org/showthread.php?t=85152