The T-28D is a fantastic plane, no doubt about it. I went from the UM Champ to the T-28 but I had the benefit of buddy boxing with a qualified flight instructor for my first several flights.
How do you like the SC? Have you considered modifying it to make it a 4 channel plane? Are you comfortable taking off and landing with a tail dragger like the SC? Assuming you are you might want to also consider the new PZ P-47 for a number of reasons. It's very close in size to the T-28 but it has additional features that the T-28 doesn't have built in (flaps and retracts).
Personally I think any of the PZ warbirds make a good next plane. In my experience the P-51 Mustang took me longer to learn than the T-28, Wildcat and Thunderbolt but that's just me