As far as I know, this is pretty common on a lot of vid cards. On my card it would not increase past 70%, even when the card was in danger of overheating.
If you are concerned about your temps download rivatuner from guru3d.com so that you can monitor your temps. Rivatuner also has a great tool for adjusting the fan speed at different temps. Just follow the tutorial they have on the site. Good luck.