Your card can stand around 100'C, so just make sure your temps are below that.
What model of your HD6850? Do you have good airflow inside your case?
Normally, 90'C is HOT for me, so try to stay below 90...
Manually increase the fan speed can help you a bit.
I installed this card in a Dell inspiron545, which has a fairly small case with poor airflow, this is not my main gaming rig but I wanted to see if it would fit and it did. I'm thinking of removing a sound card in one of the other slots to see if that will help, and its a powercolor hd6850