I investigated if it would be possible to create custom, distinct icons for OpenGL rendering buttons/menu entries by overlaying the original render icons with "GL" (which i believe to be understandable and a somewhat common abbreviation for OpenGL, at least in the coding world; given the abstract nature of the notion of OpenGL rendering we probably won't come much closer to perfect understandability anyway). I experimented quite a bit, making a lot of tradeoffs regarding aesthetics/original ogl logo color/readability/readability of the original overlayed icon, and this is where I ended up basically.
My feeling about this is:
It's readable enough, but barely.
It doesn't look too hot. :)
Its certainly better than using the same icon as for regular rendering ...
So, in conclusion, I am actually slightly leaning towards giving this another shot, with completely custom icons that do not reuse the original render icons.
As this is only a very vague tendency on my side, I would like to hear your thoughts on the matter. Fire away!
Ps.: Patch for this would be ready to go, see the attached diff.