the point I think I am making
is that even on a flat (i.e not hilly) and rough (i.e. not road tarmac) surface, an FS will be faster, reasoning being that the bumnps are soaked up by the suspension so the rider CoG is not moving as much as it would on rigid so less energy is wasted by the rider.
I accept that on the uphills, due to the much lower speeds involved, the FS is not going to come out on top, in fact I used the lock out on those
ain't gonna happen this weekend but let me know timne and place and I cna plan for next w/e or later (except when it is raining
.... I have a HRM so if OP has one too, we could use that as some was as measure of effort; perhaps swapping bike for the same stretch, otherwsie I cannot see how the difference can be quantified.
There is enough inherent dampening and spring in a decent frame, seat, bars, etc., even on a rigid, to cope with 'rough' surfaces, i.e. gravel/smaller chippings, hardpack clay, dry , mildly corrugated mud/sand/whatever.
Front shocks and a rider light in their saddle takes care of other irritations up to maybe a few inches high, and the occasional drop off, medium hit, etc. Your LEGS and ARMS are much more efficient suspension components than you will find on ANY bicycle.
For flattish non technical circuits you care carrying around extra weight and inefficiency that is not made up for by any esoteric benefit, (remembering your cog is no more maintained when you are planted on a full suss or levitating above a springy steel hardtail on your elastic body parts).
In fact, out of the saddle where necessary you are benefiting from additional factors similar to those or the larger wheeled bicycle.