I think the differentiation between "sprung" and "un-sprung" weight is probably more important that "total mass" in effecting the way the bike will ride.
The way I used to explain this to apprentices I trained was this:
Strap a 25KG weight to each foot and run a slalom course around some cones (un-sprung weight)
Now remove the weights from your feet and put 50kg in a rucksack supported by your legs and knee's (sprung weight) and run the course again
Which do you think would be quicker and easier to make the direction changes ?
