Hmm this is super strange. Could you please share the logs of PE? I have a feeling there is something that keeps failing in PE on your side and probably loops some error, which could dramatically decrease the performance.
I have been using a GTX 1070 laptop at least 50% of the time when developing PE, and it has never been an issue. Its always running in full framerate since Armin improved the performance a lot back in October. Even with 8KX, the GTX 1070 runs PE completely smooth, unless I max out Render quality at 1.5 or above then I start to see minor reprojection. For anything lower than a RTX 2080, I wouldnt go higher than Render quality of 1.0/1.25 with 8KX either way. Its quite a huge resolution already at Render Quality 1.0, especially when Parallel Projection and Large FOV is on, and barely any game will handle that anyway.
Btw, do you have any other background process running? Try quitting these if you can. Do you use VorpX maybe? It has a bad habit of injecting itself to every possible application.
Please post the logs first, and we will move on from there. (To easily export the logs, in PE go to Customize-page, then in the bottom click the “Export Logs” button and your 2 log files will be copied to your Desktop). Paste the content of the files here: pastebin.com