|"The overall airflow should not be a problem. I got myself 2 extra fans installed in the case. I'l try some cooling paste then"|
The chances of the thermal paste being the problem are slim. The problem is more likely to be poor cooling. Or it could be the montioring software you're using is simply out of whack & the GPU isn't really running that hot. Have you confirmed the GPU temp with other software such as HWMonitor?
"I got myself 2 extra fans installed in the case"
What does that mean? You didn't explain where the fans are installed or what size they are. Improperly placed fans can be worse than no fans at all. If your case has the power supply mounted at the top, all you need is one exhaust fan beneath it. 120mm is best if your case accepts fans that big. No other fans are required. A front intake fan may be of some benfit but side panel fans should NOT be used.