Per The Rocket Man:
The weight difference between a FS and hardtail seems to be a few pounds
at most. A few less trips to the pizza place for me would seem to take
care of that !!

There's a perceptible diff in responsiveness going up hills:
FS:HardTail:FullRigid.

But I find myself unaware of it until I ride a different bike.

There is also a diff in reliability: there's that much more to go
wrong in that rear sus. I've had two "walk home" suspension
failures. Both sheared off sus bolts. But I think I provoked
both through cruel and unusual treatment.
--
PeteCresswell