Don't assume those temps are the culprit just yet - 82-85°C is actually within normal operating range for a 4070 Super, and modern cards throttle pretty aggressively only when hitting 89-90°C+. Your frame drops are more likely coming from the game itself maxing out the card's memory or hitting CPU bottlenecks, especially in dense areas where the engine has to render tons of objects. Check your GPU and CPU usage with something like MSI Afterburner or GPU-Z while playing; if your GPU is pegged at 100% and you're still dropping frames, that's just the card hitting its limit on those settings. You could try dialing back a few graphical options (shadow quality, draw distance) or updating your drivers, but a 750W PSU is fine and your card being 18 months old shouldn't be an issue unless you've never cleaned the cooler.