Not if CPU limited; the resolution only matters when GPU limited (or just on the edge where you’re balanced between CPU and GPU usage). Your GPU is basically sitting there asking for more things to to, but the CPU can’t give it enough. As long as it has power to spare, you can give it more work (increase render scaling) without it costing any performance.
I don’t think there are any ways to gain more than a few FPS, but things that help:
- Make sure no background software is causing issues, e.g. anti-malware/anti-ransomware software.
- Lowering terrain LOD. This is probably the biggest one, but also one that really matters for graphics.
- Traffic usually costs some CPU; multiplayer probably also a bit.
- At least prior to SU5 hiding unused toolbar items (especially the VFR map) helped. I think that’s a bit better now.
- Glass cockpit refresh rate, as mentioned. But after SU5 it doesn’t have a huge impact for me any longer.