spookie - I'm thinking it's not such a simple question for individual runner stack injection. It needs to have all the fuel injection parts correct based on your engine specs and fuel selection. For example, a more important item is the size of the butterflies based on whether you are going to run gas, methanol, methanol and nitro, or just nitro.
As wideopen stated, the Jr. Fuel guys running IR stack injection run virtually no stacks, and their butterflies are probably 3 inch diameter or larger on a sbc style engine. Compare that to a 327ci bracket racer with an early Hilborn running gas, their butterflies are easily half the size when it comes to flow. The early Hilborn would slow the Jr. Fuel person down, and vice versa, the 3 inch diameter on the 327 running gas would slow it down as well no matter what length velocity tube was selected.
For me, if my goal is to achieve the best hp/torque for my own engine spec, I'd start with the correct basics and add parts correctly from there (e.g. pump, barrel valve, filters, nozzles, lines, etc.). Alan
