JM.02c
Your 2016 XTX Apex came with a 146" x 1.75" Back Country track new.
With that 1.75" track it needed 7 tooth x 2.86" drivers for clearance.
Larger drivers, if you have the needed clearance, are more efficient and less likely to ratchet.
If you are installing a 146" x 1.25" track you now should have the clearance for 8 tooth x 2.86" drivers.
Increasing from 7 x 2.86" drivers to 8 x 2.86" drivers is like gearing the sled up 13% and that is a big change!
The Apex 146" XTX is a big heavy sled so, IMO, if you do go to 8 tooth drivers I would recommend you change your gearing to something more around 21/37[1.76:1] as that would still allow decent top end speed but maintain good trail throttle response. I suggest changing the top gear as it is more readily available and less money. Your sled should have a 70 link chain right now but you would need a 68 link chain to run 21/37 gears.
As a side note:
I have my 136 Yamacharged Attak geared at 22/40[1.82:1] and it easily exceeds 100mph with great throttle response and acceleration on the trails.