Simhub overlay causes constant stutter despite no change to frame rate

I use rtss (or nvidia control panel) to cap my frame rate in order to avoid wildly fluctuating fps and keep a manageable load on my cpu and gpu at all times. 

With g-sync enabled, the experience is fairly smooth, aside from the known frame drops, going through certain parts of the map, going through water splashes or when one section is stitched to the next etc. All of which drops are picked up in the frame time / frame rate graph and readings. Fine. 

However, with the very basic HUD available in game, and inability to move it to the side for ultrawide screens, I want to run simhub overlay as a HUD.

It does not matter if I use full screen or windowed borderless, the presentation of frames gets immediately and noticeably worse as soon as I load the overlay. It is constantly stuttering and looks like 45fps. However, my rtss overlay tells me that I'm locked to a steady 90fps with no issues in frame time. It's like it drops sync or something. It feels similar to what digital foundry reported in the early days of release where the frame pacing appeared very inconsistent but the frame rate looked OK.

FWIW in dr2.0 to avoid constant micro stutter i had to turn v-sync on and lock frame rate *in game* (using rtss or nvidia control panel locked frame rate but did not solve the stutter). For EA WRC v-sync in game or through control panel makes no difference. But perhaps the in game frame rate lock may help?

Or you could actually put a bit of time into making some decent hud options for looks/info and placement / size option and then we wouldn't need to rely on 3rd party overlays. 

Oh and it's not my hardware not being up to the job. I have a 5800x3d and 4080 super running on a 3440x1440 ultrawide, and I cap to 90 fps. My cpu max core usage and gpu usage do not go above 75%.