smaller piston=less weight.
it takes less force to accelerate a piston in a 250cc 4 cylinder engine than it does in a 600cc engine.
so... too accelerate a 600cc 4 cylinder piston to the same rpms as even a 500cc 4 cylinder piston, you need heavier conecting rods.
and that makes the moving mass heavier...
which take more force to acclerate...
which means you need stronger parts...
so in order to produce a reliable 600cc engine, engineers needed to figure a way to process the materials they had (or come up with new ones, which in some cases, they did) to come up with stronger, lighter parts.
and to be able to do that... in a cost effective, manufacturing solution that could be reproduced a million times.
not possible back in the day.
if they could.
they would have.
edit: oh yeah. cool vid. but as usual yamaha has set their rev limit too high as it sounds like its running out of ooph before even 500rpms before.
we need honda to redesign the engine in their rr. (i'm sure there's good reason why we're waiting though.
)