This is the answer IMO. I would focus more on what you want for practical items, as it doesn't "need" any performance upgrades. Figure out what storage bags, and ski rack you want. Put on a tether, swap the carbides off and call it a day. If you want the best free performance upgrade on a Khaos - go through the suspension with the owners manual and take the time to set the springs and clickers to recommended settings for your weight. And then get an understanding of what the different settings do and dial in for your preferences.If you are new to this gig i would just buy it and ride it. There is literally nothing you need other than a tether. I would put hardened wear bars on and get rid of the carbides. Other than that, enjoy. Reallly nothing you have to have.
Get the QD2 for a drive. If you want the most solid all-around track, get the 2.6" ... if you want the latest and greatest, with the potential for more frequent track adjustments, get the 2.75"