K1creeker, thanks so much for the response. Hugely helpful..and reassuring. I am playing the waiting game and my mind simply is second guessing all my decisions. Your last 2 sentences say it all. You've been riding a very long time and the bike on 2.8s is one of your favorites...and you don't plan to sell it. THat's huge. Again, thank you for taking the time out of your day to answer my questions.Not sure if this helps, but I have the old Mach 429 trail (2018).
1) Using lower 17mm headset cup? Yes.
2) Fork travel (130mm or 140mm)? 130mm Fox 34 (29er fork)
3) crank length (and whether you're striking often or not) (175mm. Some strikes, but I've ridden it enough to know when to time pedaling in rock gardens. Not enough strikes to annoy.)
4) ever try 27.5 x 2.6 tires? (No, and I don't think I'd recommend it in either Mach 429 Trail or Trail 429 variations.)
That said, the Mach 429 Trail with 2.8s is one of my favorite bikes to ride ever, and I've been doing this a long time. This bike is staying for the long haul.