Your question about the Cube Stereo:
Own older hardtails and the Calibre Bossnut (which I love). And I tried the Cube Stereo HPA 140 (aluminium version, not sure which model year) last year. Was right away fun and fast. Perfect trail bike!
Based on that: ordered a Cube Stereo HPA 150 27.5+ frame in the winter sale and buidling this bike right now. Will be my fun full suspension bike with 2.6 rubber. The aluminium frame is the highest manufacturing quality frame I ever had. Only small detail I don’t like: the BB pressfit (no issue for the Crabon version. Carbon frames all have now pressfit…)
No idea about the 140mm Carbon Stereo. I suspect it’s great. If you have the money for it: guess you will be very happy with the bike.