We build a lot of circle track engines and where rules allow we run the longest rod we can, On our 358 2 barrel engines a 6.250 rod over a 5.7 is the way to go.
On the dyno both the 5.7 and 6.250 make peak power about the same RPM lets say 6800 RPM but at 7500 the 6.250 rod engine will make about 30 horse over the 5.7 rod engine every time.
The longer rod engines on the dyno seem to have a flater torque curve.
On our blower engines we use a 6.300 rod in those engines and those have won many championships over the years.