Personally, I would never run without an air filter. Its not worth the additional 1MPH (if you'll even get that. Look at a used filter and you'll see all the junk that would have been sucked into the engine.
If you didn't have the filter on, it would have taken oil in too. I'd fix the oil problem, put a new filter on, and be done with it.
If you aren't on L-mode, you should break 50MPH. I agree with YamaDoo - If 50 MPH is too slow for you, get another machine.