I have handled but never shot a T/C Impact. It seemed like a nice well balanced rifle, and I have to admit, I was interested a great deal in it. BUT I picked a CVA Optima instead. Just some features the Optima had that the Impact did not. Also the Optima was stainless steel and had the quick release breech plug. Again the Impact did not. And last the Optima was $50.00 cheaper.
But I am sure the Impact will serve you very well. The first thing I want you to learn about the magnum muzzleloader. Just because its a magnum does not mean you have to shoot magnum charges. Most of the claims of 150 grains of powder, while true is only hype to see a rifle. Most inlines tune in at 85-110 grains of powder. And that is all the power you need to harvest most animals.
Be sure to look at some of the older quality rifles. Knight, T/C, Lyman, Traditions, CVA, just to name a few. Many of them are reduced in price and work just fine. Use rifles in good shape are often times a way to get a quality rifle at a reduced price.