One thing that I notice in the screen shots is that each external shot shows different configuration. Coupled with Pyro's comment about following pretty much the same reasoning as Scherf had I think we'll see a little more variety in performance options for the Mossie. Right now the Mossie is essentially either clean or has the rocket rails; the bombs and drop tanks don't leave anything behind to slow it down after they are dropped. In screen shot #1 we see the old, familiar rocket rails which incur a speed penalty even after the weapons have been fired. However shots #4 and #5 show a difference from what we have, there are bomb shackles in shot #4 (and presumably in shot #3 for the drop tanks) but the wings are clean in shot #5. On page 57 of Mosquito by C. Martin Sharp and Michael J. F. Bowyer (I am pretty sure HTC has a copy of this book) it states that wing bomb carriers cost 5mph, or 9mph with bombs attached. Based on the screen shots I expect the carriers to now incur that speed penalty. So if I am right and you up a Mosquito for fighter duty and you want full performance, don't load any external stores.
If that proves to be true it will be a nice bit of attention to detail.