As you said, your tests were informal, and it is not my intent to discredit anything you determined.
I'm just posting to say it would be interesting if a pump and semi-auto of identical (or nearly so) shape/weight/balance/fit could be used to eliminate other variables. In the example given, one gun probably fits you a little better than the other and you admitted you have more experience with one than the other.
I'm curious as to how much of the speed difference has to do with working the action of a pump and how much has to do with getting back on target after the recoil and muzzle jump of the previous shot. On average, semi-autos have less felt recoil, giving them the advantage either way, so that may be hard to determine.