Trying to lap your Storm is pretty much a waste of time unless you put some deep scratches in it somehow, but lapping it will not distroy it unless you are a complete and utter fool ...................
You'd get much more out of lapping your CPU IHS, I've done several (all) my AMD's in the past with great results, never distroied a single one...........
I haven't tried lapping a Intel yet, but I will as soon as I get my new core in July (if it needs it that is) my current E4300 is making great contact with the block so I haven't even worried about doing it as of yet, but I may just for S & G's later on.
One question, have you thought about installing a back plate behind your MoBo to help support the block while tighting down the springs, it helps out and keeps the board from bowing and you can apply more pressure on the core to improve the performance.
Scythe and Thermalright both make some pretty nice ones.