I haven't shot the new TSX yet, but I have shot many a Barnes X. In my guns, they are very accurate, while some people will tell you that they are not accurate in their rifles. However, it seems that, from what many shooters have said, the new TSX, with its three rings, shoot much better in all of their rifles.
As far as the bullet itself, keep in mind that a 180 grain Barnes X is the equivalent of a conventional 165 or even 150 grain bullet. As such, you can use lighter bullets with the TSX.
Also, I don't think that TSX is ideal for mule deer. The TSX has 4 petals that open up and the bullet "drills and cuts" as it passes through, as opposed to "mushroom and push" like a conventional bullet. On elk, hogs, or moose, I think an TSX is great. On deer and mule deer, I think the TSX is a bit too much. Don't get me wrong - it will certainly work, but I like more frontal area on deer than a TSX.
Zachary