I suspect you could ride for longer and probably faster on a full suspension, even with the added weight penalty. you will loose out climbing but the rest your on a winner.
Weight is not always a penalty with a full suspension bike
My Cube Sting weighs 11.5kg, or 25.3lbs in old money
Not that heavy for a 120mm, or 4.7" travel full suspension bike
On my last ride round Welton I managed to climb higher than all the other riders on retro hardtails on one particular steep section!
Full suspension bikes usually dig in at the rear when climbing giving added traction so quite often they will climb better than a hardtail on certain types of terrain, if the climb is smooth and not in any way technical the hardtail will be faster up the hill
Yes, Full Suspension bikes can be faster on certain types of terrain and they can help you ride longer, but a bike is only as good as the rider on it