It probably depends on how much air is in the rad. If it's a small pea sized air bubble, the temps probably won't be affected much, but if it's like half the rad, that'll probably give you terrible temps.

Can you lower the pump RPM's? The easiest way is with voltage control. The slower water flow will allow the res to catch the air bubbles.

I would suggest doing the rad shake'n tilt with the rad unmounted from the case.

You could also try draining and retrying, except fill it slower, only fill the res half way full and try to keep the res between a quarter and half until the level no longer drops below half while shaking the rad.