Are you hitting the "Test" button after changing the clocks?
If so, try disabling the Test button:
Power User tab
Overclocking\Global
check "Disable Clock Test"
Don't get too crazy with this though. If you're going to use this method, increase clocks at small increments and look out for artifacts.
As far as temps, they don't throttle down until around 125c, but try to keep it under 70c, and if it goes above 80 you can be in for some problems.
Sounds like it's already a bit warm (if that temp is at stock speeds) so look into improving your case airflow and/or an aftermarket cooler. 25 degrees is a big jump from idle to load.
-z