It all depends now... are you shooting a flat object or a 3d object?
Coz with a wide open aperture, you lose DOF. On a flat object, this does not matter even if you can find a f 0.7 lens coz once you get the subject in focus, it's in focus.
But when it's 3D, you can lose the focus when the subject moves or you move. Also due to DOF, mebbe only a very think part of the subject is in focus and the rest is not in focus at all...
I have shot at wide open on a few lense and on some, they lose the sharpness. But on some, there's not much affect on it.