I don't know the answer to your original question, why developing times are shorter for some films (and why fixing times are shorter for some films). I understand the pleasure of getting used to processing times and procedures, and the reluctance to change for external reasons.
And I hope this discussion thread continues and gives us some answers as to "why" some films need less developing time, because I am curious to know.
But you've got a dilemma to solve, finding a replacement for a favorite film. I wish you luck, and would suggest you look for RESULTS. You'll get accustomed to any new process routine that is required for the replacement.
The journey I took involved quite a few trials and landed me at TMY-2 4x5 to replace 35mm Panatomic-X. So don't be surprised to find your road ahead is disruptive and leads you to an unexpected combination.
I appreciate the "difference" between a tabular grain film and a traditional grain structure, and at 100 speed there are some options for you. I'd recommend choosing between tabular and traditional grain FIRST. Then let other decisions follow.
Hopefully, your stash of Plus-X will last long enough for you to confirm your decision. Keep enough on-hand so you can occasionally check your options against your benchmark. I've found that occasionally revisiting Panatomic-X reassures me of my decision - and it shows me how minor the difference really is.
p.s. I work for Kodak (where What's Next Starts Now) but opinions and positions I take are not necessarily those of EKC.