Are Barnes TTSX tougher than TSX? My experience with the TTSX is that they are not tougher and they seem to perform the same on game from what I can tell. I feelthat the polymer tip will provide more rapid and reliable expansion on smaller calibers. The tip also makes from a bit better BC making for a flightier bullet on paper but the real world difference in trajectory is so small that it won't be noticed in the field.
I've had goos luck with Barnes X, TSX,TTSX and LRX bullets in general. They are my go to bullet on elk sized critters and up. They are not my first choice for light animals such as deer and antelope. I like something that opens a bit wider and easier for the little stuff. I good old Sierra Game King works great for deer and antelope at reasonable velocity.
As a side note;
I wouldn't go so far as to say the TSX "often" wouldn't open in smaller calibers but I have heard of it happening on rare occasion. I've shot multiple animals with a .308 caliber TSX and never had one fail to open I did have one partially open and make a 90 deg turn in an antelope once though.