When looking for a CPU for a server that sits in my living room, I went down the thought process of getting a low tdp. I don't have a quote, but I seem to remember coming to the conclusion that tdp is the max temp threshold, not the consistent power draw. If you have a computer idling I believe you won't see a difference in temp between cpus, but you will have the performance when you need it.

These days, a quiet, pwm fan with good thermal paste (and maybe some linux CPU throttling) more than achieves my needs for a "silent" pc 99% of the time.

I would love to be told my above assumptions are wrong if they are.