Went from hardtail, to FS (medium travel, then short travel and then back to medium (140mm) again) and am now riding a 140mm hardcore hardtail (identiti aka) with 650b wheels. Happily ragged it down the trails around Hebden (steep, rocky, muddy) and on trail centre reds/blacks without noticing any reduction in speed (I’m reasonably quick).
Given that I’m not into riding huge drops or massive jumps, the only real difference in terms of my riding (and I’d suggest the majority of people on this site) is that when the terrain gets bumpy you don’t have the benefit of the rear suspension tracking the bumps and keeping that wheel glued to the ground. That means less comfort and less control as the rear end of the bike is being bucked about more. However, If you spend most of your time on terrain like this out of the saddle (I do) then you learn to use your legs to absorb more of the chatter. I also reckon that it is probably faster over your typical swoopy trail centre terrain as it doesn’t have the absorption mentioned above by jedi. To me this means that it gets spat out of corners and compressions faster than a FS as none of the energy is being absorbed by the suspension. However, this is speculation on my part and I have no scientific evidence to back this up 😉
Being a 7005 aluminium frame with the Superstar/Pacenti Tesla TL28 wheels, it is also seriously light and climbs like a goat on speed/fire/crack – delete as applicable.
I still have the 650b FS bike (transferred parts from one to the other) and will undoubtedly build it back up and keep using both, but right now if I had to make do with just the one it would be the hardtail.
FWIW the Infiniti AKA is superb. Climbs well, descends superbly and corners like it is on rails, as well as having a relatively slack head angle, short chainstays (great for popping over obstacles) and being optimised for 140mm forks. You can pick up a frame headset combo for £300 and it takes both 26″ and 650b wheels.