A few things you can do to lower temperatures without losing much performance:
- Ensure there's plenty of airflow in the case
- Set an aggressive fan curve both on the video card and the case fans.
- Consider setting an FPS cap to the monitor's refresh rate. Unless you're trying to go for benchmarking scores, there's little to no practical benefit of performance exceeding the refresh rate all the time
- If you're using an NVIDIA card, use Afterburner's OC scan to figure out a higher VF curve to start, then cap it at some point. Yes, you need to do an OC scan because the video cards operate on a "what clock speed can I get at this voltage?" principle
- Play around with the power limiter. Sometimes the video card may not offer an appreciable performance benefit operating at 100% power. In a personal example, I have a game that runs more or less the same at 75% or 100%, but it'll happily use 100%.
Also keep in mind that 75C-85C is an expected range for video cards to sit at when given a reasonable load.