Sorry but you guys are missing the point.
Multi cylinder engines are easier to pull higher revs because the forces of the pistons are acting against each other smothing out the oposing forces.
The more pistons you have the greater the piston area. More piston area you have the more horsepower you can get.
If you use F1 as an example, Back in the 70's the Ferrari V12's had more horse power then the Cosworth V8's but the V8's had more mid range tourqe.
Ducati built a Super single in the 90's which was 600cc i think. They cut 1 of their V-Twins in half but they left in the unused conrod to act as a balancer.Other wise it would never have been able to pull such high rev's.
So in short, the more pistons you have the more power you have & the more pistons you have the higher the revs you can pull & the higher the revs you have the more power you have. In theory.
A modern 250F pulling 13,000 rpm is definatly over stressed