You could try adding additional fans to your system to lower the load on the GPU funs, then they could run at slower speeds. You should just make sure your VRM temperatures are in check too - some GPUs have sensors for the VRMs and their temperatures will show up in GPU-z. I'd try and keep VRM temps below 80C.

You could also try downvolting your card - that way it would take less power, and the fans could run slower too.