Arctic MX-4 is the most universal thermal paste I use. MX-5 was released lately and it seems to be good choice too.
IHS doesn't seem to be aluminum so probably liquid metal would be the best, but it's extremely difficult (and dangerous) to apply so I don't recommend it.
I didn't delid my console yet and I don't see much difference between Noctua NT-H1 and generic silver thermal paste, maybe 2-4*C.
The dies and chips are pretty big in PS3, especially in phat models. Heatsinks are very basic and heavy too, so heat accumulates on them and very small differences in fan speed results in temperatures change.
Basically every thermal paste will be sufficient, it's more about longevity of them.
What really makes difference is application of thermal paste. If you make layer too thin, you will not get full contact between IHS and heatsink, if you apply too much you will raise temperatures too. I did thermal paste replacement recently, testing three times and very thin layer on both IHS and heatsink was the best, just enough to make contact. "Pea-sized blob" didn't spread it evenly, and applying with cross method given 3-5*C higher temperatures on RSX.
I prefer console running quiet than cool so I use Syscon fan profile and it keeps under 75*C most of the time. I get annoyed by WebMan stepless control.
If you run fan like 40% minimum, there probably won't be any noticeable difference.
