Every XTP bullet has a specific velocity window. Too slow and you won't get very much expansion, too fast and the bullet will break up very rapidly. Off the top of my head, the 240 gr XTP will expand reliably between 1000 to 1500 fps. The 300 gr. XTP is a stout bullet and should be kept to at least 1100 fps muzzle velocity in order to achieve proper expansion. It is, quite frankly, more bullet than you really need for deer hunting. I personally stick to the 200 or 240 gr versions of the XTP for that purpose.
In short, to answer your question, the faster you push an XTP the more it will expand. Again, assuming you stay in it's velocity window. On deer, it probably won't make much difference if you hit hit shoulder or not, bullet performance should be good either way. You may want to check out Hornady's website to see what the velocity windows are for each specific bullet.
As far as cast bullets go, you probably won't get any expansion at all, but they'll penetrate like crazy with velocities between 900 and 1500 fps. Some peopla swear by cast bullets for deer hunting; I do not. I like some expansion on deer. If I were carrying my .44 for bear defense, then I would probably use a heavy hard cast bullet.
I hope I have helped some, and not confused you. I have a great deal of experience loading for my .44, so please feel free to ask more questions.