If it was lapped on the first day, then there is probably no basis for comparison.
Wow, at least one person who can read. Yes, i boot it up, to make sure that it runs, and test is a bit, then start lapping it for several hours. Once the lapping is done, installed and tested to make sure all other related stuffs are done right. In short, I really can't have basis for comparison.
And how did the temps work out? significantly lower? Low enough to risk being SOL if your processor craps out and you need to return it? Sorry i will keep my warranty.
I can tell you how good the lapping job is, but I really can't tell you how good the CPU performs after the lapping. It works, and technically lapping doesn't change the performance of the chip, and that applies to heat generation of the chip.
As to better contact, I will say a poor application of the thermal paste can have a bigger impact on contact, and therefore temp. I tried many different methods and stayed on the ones that works best, yet I forgot which method was that. Hey, I wasn't going to write a book about it. The fact is, since the actual spreading happens when you put the HS on the CPU and won't be able to see how it spread until you remove it, you will actually have no idea how it spread. Now does thermal paste spread better on smooth surface than rough? I will say no, but that itself can be a thread.
So regardless of how good the lapping is, you still needs to put Thermal paste on it. However, if it is lapped well, then the amount of thermal paste needed is, in theory, reduced. Because of that, applying thermal paste on lapped surface is far harder than lapping the surface.
After you have done all those and question all those, you would have run enough tests that others probably will never do in their entire life. In fact, this is what Overclocking is about IMO. Instead of working with a lot of variables at once, you focus on resolving a variable at a time. To me, make sure that the heat generated by CPU as well as all other component radiates properly is the third thing to do before OC (the second thing is component selection and make sure that they work under specification, some may take one more step in modding components to secure stability related issues, and the first thing is to read instructions, and specifications).
In comparison, the time and work to lap CPU is minimal as reading and part searching can take up to weeks individually. Lol test.
Does it worth it? It varies upon people. Again, the time and work of lapping is really small in comparison, and relatively safe. I will say changing resistors are more dangerous, and pencil mod is 1000x more dangerous than lapping. Some of my friends actually brought silver ink pen for the job and we ended up with arguments because I argued that changing the resistor is easier and safer blah blah blah.
Is it worth it for me? Of course, the fact that I lapped it right makes it worth it. Yes, after spending hours lapping your newly brought CPU against different sandpapers with water, it is actually rewarding to see the CPU still works.
Is it risky? Nope, not in comparison. Never even heard of someone breaking their CPU by lapping it.
Return when broken due to lapping?
http://www.youtube.com/watch?v=lrF5x1OSJuQ
You will know the answer after the first pass of lapping.