It's all to do with piston speed. The total distance that a piston travels in a nominated time.

With a 50mm stroke [for example] you could rev it twice as fast as another engine with a 100mm stroke & both would have the same piston speed. [total distance traveled in a unit of time]

If it's ultra revs that you want, then some of the speedway blokes apparently use the A14/15 block, but install an A12 crank along with rods & pistons from something else.
With the 70mm stroke & the longer rods that these tall blocks allow, the rod angle becomes more favourable & they seem to buzz quite happily at 10,000 but personally I'd go with the A15 & keep it under 6,500 for street use & use the extra torque that the longer stroke provides, then just stick it in the next highest gear & haul arse.

But that's just me.