George, my reasoning with the TTSX is that I haven't seen very many of them blow up, lose a petal, or in any way deteriorate from the pictures I've found online in any caliber, against game or test media. I'd like to test them myself in my WSM to see if they can be pushed too fast for their construction (I.E. deform, over-expand, and/or under-penetrate). Secondly, I want to see what kind of expansion and penetration they provide in comparison against the TTSX's of heavier weights ( I also have the 130 and 140's). If they are found to hold together at magnum speeds, penetrate at least 12", and expand to the same diameter as the heavier versions, I can't see a reason not to use them at higher speeds than their counterparts on deer, or even larger moose-size game for that matter. I think you have a perfect bullet for what you intend on hunting, I'm just interested in trying this out. My round of choice for next year's moose hunt was going to be the 130 or 140 TSX as well.
The typical reasoning for using heavier bullets for bigger game is (IMO) they hold together better at higher speeds (don't separate from the jacket), penetrate further (due to more energy, and lower velocity creating less expansion). So if you find a lighter bullet that can still accomplish both those tasks, why not use it? The only exception to this would be long range hunting, where you want a bullet with better ballistics (generally heavier) to ease wind correction, and retain stored energy.