[Mach 1]

That screen probably wont make a noticeable difference no matter what, and I wouldnt worry about it that much. Some say remove it is better, as your thinking dictates, and others say leaving it in is better, as it smoothes the airflow(less turbulence). I think I even saw a dyno test in a magazine where Horsepower improved with it in, but that doesnt mean much. You cant believe anything you read in stang rags.

I would just get an aftermarket MAF meter anyway if you really want to increase performance. That is the best thing to do, and you dont have to worry about the screen at all then.