I NEED to pee Harder/Faster ???

For hand lapped blocks I doubt you'll see much difference between 600 and 1200+ grit. People have even reported lower temperatures from a mirror finish (theories on this usually involve artic silver's high viscosity causing it to form a barrier layer instead of filling the micro-fine scratches).

"theories on this usually involve artic silver's high viscosity causing it to form a barrier layer instead of filling the micro-fine scratches"

eh ?

so then Sin Etsu would be much worse ?
(retire that 'theory')

A question on mirror finishes using brasso, autosol and the likes
how do the chemicals accomplish their purpose- by 'filling' the marks on the surface, or by acting as an abrasive?

They do so by acting as an abrasive. Brasso contains a superfine abrasive grit suspended in a hydrocarbon/ammonia solution which acts as a "lapping" lubricant. The grit just skims off the top rough layer of the surface and assuming the surface was reasonably flat and smooth prior to starting, will give a shine. When the liquid dries out you're left with grit flakes that just dry out and wipe away.

I make no claims as to the accuracy of that. I personally tend to lap to 1500 grit and use a method similar to cathar's (looking at something reflected in the surface) to eyeball flatness. It's not hugely accurate, but it's good enough.

I see, thanks Cathar
so essentially those products aren't terribly effective unless you were to use a process like that used to polish cockpit windshields