Nah, increasing that wouldn't increase performance with Virtu I don't think.
What Virtu MVP does, mainly, is provide smoother V-Sync performance (less tearing), from what I know about it. That shouldn't really be affected by the iGPU frequency at all, I wouldn't think. It wouldn't give you more FPS, or anything (because it's V-Sync, obviously).
Also, if it's just normal Virtu and not Virtu MVP (Z68 instead of Z77), you'll actually have worse performance with Virtu enabled. Normal Virtu is kind of a fail in that department.