stratix ii survive at high temperature 150?

Yes you are right, I meant specifying the temperature conditions.

For the extra margin, go to Assignments > Settings > Fitter Settings, and in the Fitter effort block, select "Auto Fit" and put the margin in "Desired worst case slack".

I think you'll have to check yourself in the Timequest report that this margin was met on all clock domains.

It is hard to give any specific margin value you should use, I don't know how slower the design can be when going from +125°C to +150°C. I recommend to have a look at the Timequest report, and specifically the "worst case timing paths" report, and try to design some tests you can run at +150°C that make extensive use of those paths.