Had an XTi but for some unknown reason sold it
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I do have a Charge ALX which has the double bit holders. They would be are great IF you really use a variety of bits often. You can keep the bits you use ready to go in each holder. Not having scissors wont be an issue since you'll be running your Center Drive, more on that tho.
Now you do loose the flat driver of the TTi by going with the XTi. To me the biggest deciding factor is those double bit holders and IMO loss of the flat driver. I don't use 2 particular bits so often as to need to keep them ready in bit holders. I do use the flat driver enough tho so the loss would be notable.
Knife steels. S30V vs 154CM. So heres my take. We like what we like for any reason and no reason at all. We like what we like. I like both so its a draw for me. Keep your edges tuned up and you'll be fine with either. Heck even LMs 420 is good so long as you keep it tuned up. They all cut and cut well. Try to not let any marginal "advantage" that one might have over the other that most would not notice influence you. Even those who rigorously test for the sole purpose of edge retention, ease of sharpening, toughness, etc only show small overall percentages of difference.
We like what we like. If you like one over the other then lean in that direction. If you have no real preference then lean to the range of implements that work best for you. I like the nicer steels as much as the next person. Between 154CM and S30V
both are great.
So if I were you, I'd chose the tools that best compliments your Center Drive + AND can stand alone. To me that is the TTi because it has scissors.