What stroke crank in BBC

In a multi engine modified pulling tractor with blown BBC with 4.5 bore what stroke crank 4.25" or 4.5" would you use.

 

I run a stock 4.0 stroke crank, If I am going to increase piston speed it will be in RPM not because it has farther to go in a revolution. Also in going larger in displacement makes the same size blower less efficient. Then you have to spin the blower harder to make uip for the displacement.

 

Ageed. When you get into 4.5 stroke on a chevy without a raised cam, things start getting pretty close - lots of check and recheck on cam to rod clearance, etc. RPM vs. torque for your application would be the decision to consider.
If you're on alcohol, take the compression to 13:1 with less stroke to wake up your combination (be sure you've got a tight seal on the heads).