I say lap neither. I've never seen a CPU IHS thats so bad that it needs lapping. Add in the risk of damage (smaller now that the pins are on the mobo) and I can't see why you'd try. I would only lap the HSF if its not flat. I'm not talking about lines, thats what the TIM is for. I'm talking about those HSFs that are so concave/convex that you wonder how it ever left the factory. I have never owned one, but I've seen picures online.
You have to remember that as long as you use a quality TIM, you don't have to worry about small imperfections. Quality TIMs contain silver, which is an excellent conductor of heat. So as long as your HSF isn't totally warped, you should be fine.
#2 If you do or do not please explain why..and yes I know that lapping the cpu voids warranty.
#1 Of course not, everyone has their own reasoning behind the decision to lapp anything.
I'd say sure if this was the official (CPU and Heatsink Lapping Club), but its not, more than likely only THGF users that have successfully performed the lapping process and know whats involved, and the gains or possible damage, would even be the encourager of lapping in the first place.
#2 The why is obvious, lower temps, higher overclocking headroom, and since you already know lapping instantly voids the CPU warranty, you may be soon to join the Unofficial CPU Heatsink Lapping Club yourself, as curiosity killed the cat, so to speak, educate yourself thoroughly before you decide to dive in, if you even do.
I lapped my Xigmatek S1283, and my Q9550, added an additional 120mm fan to the Xiggy for a push pull airflow setup that resulted in a 10C drop in temps across the board, even better than I had hoped for allowing a rock solid 24/7 3.83G OC of the Q9550.
Also closed the gap of the differential core temp reading across the 4 core temperatures, where Core Temp reported a big variation between Core 0 & 1 readings and Core 2 & 3, those readings are now constantly within 1c to 2c of each other., depending on core load.
Thats what happened for me, theres no guarantee you'll get the same results, lapping is serious business, you cannot undo it, don't forget that.
I'm a definite Go For It, but my lapping experiences so far has yielded great results for me, but educate yourself first! Good Luck if you do! Ryan