Hi Martin and welcome to Toms Hardware Guide Forums.
As for myself I just got sick of dancing the CPU shuffle, waiting for one of the camps to officially release a 4ghz CPU, and once you overclock to the 4ghz level and experience the amazing speed, regarding boot up, desktop performance, application response, it will totally spoil you.
Then going above 4ghz is totally brain boggling and you just find yourself not satisfied at the lower speeds anymore, but that's my own personal preference, it's like getting your favorite candy and after 2 licks having it taken away.
Nice overclock you're sporting by the way!
I know that candy is not a good example but those of us that do run the higher clocks have simply spoiled ourselves and don't want to run the slower speeds anymore, mainly because we pay extra for that privilege.
You cannot do it with just any stock cooling solution, the key to running higher clocks 24/7 is you have to keep it cool and stable, and that's an added expense, overclock-able hardware is also an added expense, and of course the added electrical utility expense.
That all has to be an acceptable factor to the 24/7 constant core clocking, now regarding your 2nd question, that's too hot as far as I am concerned, I like it as cool as I can keep it, but that's just my opinion!
Ryan