I have used the new TriX exposed at ei 400 and developed at 68degrees for 12.5 minutes. This is the same routine I often used on the old TriX. This time and temp works best for me when the light is a little flat or low contrast or the subject is not highly reflective. This doesn't work as well for me if the lighting was high contrast or the subject was highly reflective, if so I usually reduce development time one to 2 minutes. It sounds like you may have more than one roll of film to develop, you could always develop one roll or part of one roll and make adjustments from there if the lighting was similar on each roll, or you could go out and expose another roll the same way in similar light that you are willing to sacrifice and experiment with that before developing the rolls you have in mind, if the original shots you took are really important to you. I don't know how far you plan to enlarge, but the difference in grain with XTOL 1:1 and 1:3 is very minimal in my opinion, if noticeable at all up to 11x14, and to me, enlarging beyond 11x14 with 120 film doesn't work well.
Good luck,
Doug Webb