I have the Niner RLT RDO 4-star (Carbon). I’ve been on some fairly challenging technical single track (more technical than my off road riding skills warrant) and haven’t cracked the frame. I have the OEM Stan’s wheels with 38mm G One All Arounds and a set of November RCG36 wheels with 30mm Pro Ones for road riding. Works well for me.
Edit, Bikebling has the 2018 version (like mine) for $3,199. I’ve never bought from them, have no idea who they are, but that’s a heckuva price for this bike:
https://www.bikebling.com/Niner-RLT-...4-18-47-55.htm
I realize this is over your budget though.