You have a double edge sword. The longer barrel may not be any more accurate but you'll pick up some velocity which at the distances you describe will be a big deal when you trying to compensate for drop. So it could make you more accurate.

Here is how I see the experiment going if hypothetically you'd conduct one. You have to choose a bullet, a brand of brass, a powder and a primer. Shoot a batch of bullets using the same gun with multiple barrel lengths and choose the one that had the smallest standard deviation for velocity. That would be your most accurate barrel length for given cartridge.

I've heard quick and dirty that one inch equals approximately 50fps.

The end all, go with what you're comfortable with.

Tom