I think the K62 is better than the CM690II. They're similar market targets as well, personally I went for the K62 over the 690, and am not regretting it.
The R3, is what you want for quietness though. Don't get me wrong, the K62 isn't too bad, but I changed the default fans, and still I thought it was quite loud compared to my old HP media centers (although these are supposed to be quiet). Saying that, now I don't even notice the noise. As for airflow, My 2500k has never gone over 50C (with an A70) and the 480 has never gone over 80 from what I've seen.
kd