Tigger-
it is a physical limitation of G-forces (acceleration, deceleration...repeat)
When you think about it...at 7500 RPM, each pisting is moving up and down 31.5 times a SECOND!
Think about the interial loads of accelerating a piston and rod, up to TDC, then the inertial forces require to stop it, then start it moving down...then stop it at BDC, then accelerate it up to TDC again..(repeat..etc.) 31.5 times a second. The G forces working against the metal are litterally around 5000 to 7000 G's.
If you have a shorter stroke, the pistion has less distance to cover from TDC to BDC. This means that this piston is moving slower while doing the same 31.5 cycles per second. So shorter stroke, allows for higher Reving, but means less torque.
A longer stroke has much more distance to cover from TDC to BDC, and so it must move much faster to cover the same 31.5 cycles per second. This means higher pistion speeds, which means higher intertial loading, which means you cannot rev as high.
Thing of the force required to just STOP a pistion that is moving fast enough to cover the stroke distance 31.5 times in on second...that pistion is really movin...it wants to keep flying up past TDC, and past the valves and right though your hood to the moon....the only thing that stops it...the pin holding the piston to the rod, and the attachment of the rod to the crank...and the crank itself as the theoretically unmovable object (but it does move).
Anyway...I'm doing a lousy job of explaining it. The article I have does a MUCH better job of explaining it...When I find it, I'll post it up here.
7500 is just a figure I picked out of the air, I do not know how safe even 7500 would be with our long stroke engines...
Leave it to Random to Needlessly complicate things.