This is the situation simplified.
Two identical cars with programable engine management system except one has 20lb/hr injectors and the other has 60 lb/hr injectors. Both are tuned to 15 : 1 a/f ratio at cruise.

Which one gives the best economy.

My experience is that the 60lb/hr gives worse fuel economy, maybe because of poorer fuel atomisation.

Has anyone else experience this.

 

With the correct tune - They will be the same.

 

In theory, the longer on time of the smaller injector would allow the fuel to mix more evenly in the air stream and yield more complete combustion. I don't really have any data to support it but that's one angle of looking at it. The differences between those two injectors probably wouldn't be so bad. Now a 20 vs. a 160, that would probably be a pronounced difference.

 

If the 60lbs where high impedance and the engine was small enough cubes, even the minimum pulse width could result in too much fuel at idle. You could get your 15:1 at cruise but idle would be rich and driving around town would lower mileage.

 

On my SS, my 42s get EXACTLY the same mileage my 26's got.

 

Which his why you would have to get a rising rate FMU greater than 1:1 to lower your fuel pressure at idle (while still maintaining proper pressure at WOT). The lower pressure would allow greater pulse width and pretty much alleviate the problem.