So I just tested this with the two devices I have with Intel graphics.One is my work notebook (it's technically an Optimus hybrid of onboard Intel 530 and a GTX960m), the other is my GPD Win (Intel Atom with onboard graphics).
First of all, I cannot reproduce any framerate drops in Rightful Property. The GPD Win goes from 19-20 fps to 21-23 fps. The notebook stays just under 50 fps in both cases. Looking at the logs (r_logSmpTimings), I can see a fairly significant reduction in frontend drawing duration on the notebook, which does not increase the frame rate because the backend stays the same and limits it.
Unfortunately, the notebook also shows some serious graphical artifacts with the vertexcache version. I tried different versions of the Intel driver to no avail. The GPD Win is fine. The Nvidia card on the notebook is also fine.
You did not see any visual artifacts, right? They were fairly noticable, so you'd probably have mentioned them. As for the performance, can you give me more information about the graphical settings you are using? Resolution, AA etc. as well as shadow maps or stencil, ... And what build are you using, release x86 or x64?
I'm not sure where to go from here. If the changes cause performance drops or even visual artifacts on some machines, then I'm not sure we want to apply them. But I don't really have a clue how to fix either.