The Summit sides are set closer to the stove aren't they? The T6 has curves in the sides so they stick out a little further. That extra distance may make a big difference in temp, but I erally wouldn't be concerned with either. It's a wood stove - it's supposed to get hot. Either stove will provide the same amount of BTUs, put out through convection, and sides that are much cooler than a plain unjacketed stove. Side temps depend more on the length of time burning and temp of the stove than on which model it is. If you don't want it too hot you can make smaller fires.
If I fire mine up (pun intended) I'll see if I can touch the sides after it's going for a while.
If I fire mine up (pun intended) I'll see if I can touch the sides after it's going for a while.