1.375 should be your upper limit on a good aftermarket sink.
1.4 is not recomended unless you can keep load temps very low.
1.5 your asking for it.
Idle temps, ummm you dont really look at a system like that, unless your looking to see if you mounted the sink properly.
Load temps. This is where you want to pay the most attention. You'll hear different numbers from different people, however the general concesus from most people was you keep the cores under 70C load.
If your super scared, as i said, make sure you DO NOT set voltage in bios higher then 1.375, make sure you get an aftermarket sink, and be gentle with it. It should outlast its lifetime this way.