Feel silly asking this build question but can't figure it out!
For the following motherboard and CPU, is thermal paste required? The CPU comes with stock heatsink/fan but no thermal paste. Intel CPU manual doesn't mention thermal paste at all. However, the motherboard manual does mention thermal paste.
Agree. To make sure, see what the CPU installation instructions say. If it just says to mount the HSF, then it already has thermal paste applied.
I have a slightly different opinion about thermal paste for aftermarket HSF. Unless you're trying for a massive overclock or the HSF doesn't come with paste pre-applied, you don't need to buy thermal paste. Special pastes don't really do a whole lot (I believe some of the best are only 4 degrees cooler), so they're not really worth it until you're pushing the absolute boundary of what the CPU can handle.
I mentioned buying thermal paste with an aftermarket HSF because some don't come with thermal paste. If the cooler comes with thermal paste, MadAdmiral is right. The nice thermal paste like MX-2 will only drop the temp by a couple degrees. I have a bunch of MX-2 in my stash of building equipment, so I always replace the stock thermal paste with it, but it's not required.
Use your common sense, though... check to see if there's any thermal compound on the HSF before you stick it on there. It should be fairly obvious... I could be wrong, but if you don't see any, than that should tell you that there probably isn't any pre-applied. This should probably hold true unless Intel either came out with invisible thermal compound, or they used so little of it that you can't even see it. I highly doubt that either of those are the case.