I just realised "why we have not seen that", because we do not have any 3GS here to try it on .. I wonder if that slowness could have something to do with 4.3.3 ( is a recent update is it ? ) and/or if Mino Rescue and Minotron are still going fine on it.
I have to check some stuff later, only "solution" I could think of ATM is to try to give you another build with "a couple of things changed" and see if it makes any difference.
Really, this is puzzling "there should be not much difference" not in terms of the graphic engine at least I wonder if it's a memory issue or something.
Thing is that "normally" if it goes well on the iPad ( 1 ) it goes even better on the iPhone 4 we do test on both and adjust things to be sure it all goes well on both but yeah sounds like we miss the 3GS ..