I run in D3D, I do notice it runs
slightly faster on my pc in OpenGL though. The reason I stick with D3D is because when running in OpenGL if someone has the shieldbelt it's not diplayed as such until I'm
right on top of them practically. It's no fun running up on an "easy kill" only to discover, much to your horror, they're sporting 100 health / 150 armor...

This
may be just an effect of the particular driver/hardware I'm running, give it a try for yourself.