Warren,
I have this combination and I am running it in the ANTEC NSK2480B. This overall combination is great. As far as how cool and quiet it is, I can tell you this. When building the unit when I first swiched it on I was amazed at how quiet it is, and that was with the cover off the case. At one stage I left it running, went a had dinner and because the screen had gone into standby I went to swich the whole thing back on because it was so silent I thought it was not on.
Overall it does run cool, but I think that is aided by the case. The NSK2480 has two 120mm fans located new the the CPU on the mobo that have three settings on them, the slowest setting is wispher quiet (the fastest is a little noisy). The case is really well designed and with this set up the slowest setting will be enough.
With the ANTEC Minuet 350 (I have this case for my main PC), it is a great case but the fan does make a bit more noise (there is only one compared to the two in the NSK2480) and the airflow does not seem as good so the system does run hotter... but then I also have an AMD 6000+ in that case.
With the Encoding, yes it will be good enough, just don't try and encode while watchng one HD channel and recording another.
Overall the GM-MA78GM-S2H & 4850e combo is a winner.
Hope this helps.
Arkalore