Try `setrendermode 0` in console. Use 3 to go back if not through menu.
Full list but only 0 and 3 are available:
0 - CPU: Classic/Software
1 - CPU: n/a: Polymost flatshade prototype
2 - CPU: n/a: Polymost textured prototype
3 - GPU: Polymost/GL
4 - GPU: n/a: Polymer

We ditched classic as a menu option as it scales really poorly with higher resolutions.
Plus Aftershock utilizes quite a few larger transparency effects and design elements that are pure poison to software rendering at a scale but extremely trivial to any sort of 3D accelerator. (i.e. smoke)

From my experience, you can still do 1280x720 with relatively good performance and some times even better than GL with TROR scenarios. But these caveats are rather hard to communicate clearly, plus being able to replicate pretty much 1:1 software look on GL side reduced it to a choice of performance only. (Yes, even y-shearing can be enabled on GL :) )
FYI: Aftershock goes a little more bold with sprite constructions and around the last few months we focused more on getting the game done than wrestle with sprite constructions to reduce visual glitching, so you might see a few more oddities here and there compared to the base game.

Intel HD is a bit of an exception since it has quite a few architectural and driver level bottlenecks compared to something like AMD or NVidia stuff from that era. OpenGL is getting less and less supported I think and even sandy era GPUs with modern drivers no longer work with GL properly.
We did do some optimizations early on during preview days for those.