I have a G40, with a Vortex Razor on mine. Mine shoots around 2" groups, at 25 yards(free hand), and most of that is on the shooter. I also have a 6" KKM Precision barrel, originally purchased for my G20 SF, that I have tested next to the factory G40 barrel. It might be a bit tighter, in group size, but I sure wouldn't want to live on the difference. When I shoot from a custom pistol rest, at 100 yards, I get about a 5" group, with my 180 gr. XTP full power hand loads.
About the only thing I can say on the trigger, is make sure it has a "-" connector(I believe that is suppose to be factory stock in the G40), and do a 25 cent trigger job, polishing the mating surfaces of the Glock Trigger assembly. You might try an after-market connector, like a Ghost, but reviews are mixed on them. I have one in another Glock target pistol, and it lightens up the pull force some. I probably wouldn't run one in a pistol that I needed to be completely reliable, but the one I have is decent in that target pistol.
As 10mms go, the G40 is a nice pistol, in my hands. I have a G20 SF, and a G40, and my two son's will probably be fighting over the G40 when I die.
Squeeze