I have read on another Forum (24hourcampfire), that for the most part, the TSX requires higher velocities to expand. The TTSX has the polymer tip which increases the BC, and also initiates expansion. The cavity under the tip is larger, therefore the bullet expands better at a lower velocity.
There are over 200 replies to that post on that Forum, about half love the bullets, half hate the bullets. There are pictures of recovered bullets showing no expansion and the bullet nose bent instead of expanding in the TSX. Lots of stories relating to small entry and exit wounds, but as people reply that if you recover the animal to see the entrance and exit wound, did the bullet really fail??
I have never used the TSX, but I use the 168 grain TTSX in my 30/06, and have shot two whitetail deer with them, one ran about 10 yards, the other about 30 yards. No bullets were recovered, and exit wounds seemed small, about twice the size of the entry wounds. I will continue to use them. For Elk hunting, however, I use the 210 grain Nosler Partition in my .340 Weatherby.