for the thermal paste you should start using the
IC Diamond paste
this is much better then the AS5 - all you got to do is warm it up a little before use because its so thick, but diamond is the best conductor of heat by far
Thermal conductivity - Wikipedia, the free encyclopedia
Silver and Copper being around 400 W(m-K) and Diamond being over 900 W/(m-K) - I have mentioned this before in another post about how I made my own with ground up diamond dust and some other stuff, but now there is some that is made already and works great
only problem I see is that its not a "glue" so it cant be used to connect it, you would have to have some sorta way of screwing it down - probably a whole redesign of the heat sink and such but it might not matter if the heat isnt really that bad - also maybe just fasten the led to a piece of copper somehow with thad diamond paste and then thread it into a larger heat sink or fasten it to that somehow