Thought the claim was the X's expand down to about 1,700fps or even a bit lower than that in .45 cal. and down to 1,900fps in other calibres.
I used to load the 350gr. "X" in my .458 2" at 2,290fps and felt OK to 300 yards, as easy poke for moose/elk or deer/bear with that rifle due to the high BC. The bullet was exceptionally accurate with sub 3/4" groups at 100 meters. I suspect the 350gr. TSX should be similar. Never got a chance to use it on anything with those bullets, though. The 400gr. Barnes Old Style bullets are quite good ones, FN for lever guns and pointed for bolts or single shots. The 400gr. Barnes is also very accurate. My buddies 18 1/2" stainless Marlin gets 2,007fps with 49gr. Re#7 with the FN Barnes 400gr., no pressure signs at all. Cases literally will fall from the chamber - fired cases, in and out.