Do you think you get an actual accuracy or group size boost by switching from a 4 to 6 inch barrel?

I know ive read about "testing" dont by a PPC gun builder in the 1980s that decided that dropping to a 4" only resulted in about 1/8" increase in group size.

But that same builder determined shooting 38 wadcutter ammo in a 38 special chamber decreased the group size versus being fired in a magnum chamber about an 1/8".