openarena's technically higher detailed than Q3A as well. You might want to at least turn the texture detail one notch down and geometry to medium to get closer to Q3A specs.
this isnt completely true, as what the OP said OA's assets (maps and models and such) run just fine with other executables. the fault is purely with the new executable that comes with 0.7.6. in which case lowering the graphics settings will probably help, but not completely remedy the situation. a better solution is to simply use a different executable with the 0.7.6 assets until a better executable is released.