Thank you for reply
The HSF that came with the 965 is 70mm and held in place by 4 plastic clip/prongs. You put small screwdriver flat head and push it only a little and it lets go grip on the fan. Do this two times on same side for having it let go and the fan slips loose. It is very easy.
The 80mm fan I try is also AMD that came with Athlon FX 60 or 4000+ and has AMD logo on it.
Removing clear plastic has fixed all cooling for the machine. I play Unreal Tournament 3 with both GPU’s active and physics on at high resolution and core stay under 60 in worst case and fan near or some above 4000 also worst case, when room itself is 75 F or 78 F temperature also.
So stock HSF is now sufficient even with a dual GPU GTX 295 under full load located under the CPU and heat from card rises and affects CPU to make it warmer I think but now that does cause no problem with heat and fan noise.
I buy from CyberPower and so feel good that it works as shipped without need to remove the Heat Sink at all, so warranty is still valid. They seem a good company and I am glad to have purchase from them. Next time I will if I can order one again ask for a more advanced HSF but one they install so that too is under warranty.
Thank you all for helping