Probably the most helpful/indepth analysis I've found was by noneother than torukmakto4. His findings can be viewed here. In a pinch, his findings are quite clear although they only pertain to the N-Strike Elite Retaliator barrel. It's best summed up in this comment he posted.
"It is a given that "guide barrels" can only act as a velocity reducing device. Usually, velocity and range can be considered the same parameter, so the usual observation that the smaller-bore extensions reduce range test results makes sense. Effective range and accuracy effects are more complex, though. If you are going to properly quantify them, you must account for the instability of many of our darts at higher velocities; in a very common situation such as a 100fps Retaliator or Stryfe, nerfing the muzzle velocity slightly will often itself yield an accuracy increase independent of any other effect (such as correcting initial yaw, or reducing the effects of muzzle blast on projectiles, which have both been theorized about with these barrel extensions)."
I'd say that barrel extensions like the Longshot and Recon are probably a waste at this point. Longstrike and Spectre barrels haven't really done a lot to effect much of anything because of their diameter. Numbers have been crunched on the Retaliator's controversial "rifled" barrel enough to be helpful for stock AND modded blasters. So if you are going to use one, use one that's useful to you.
As with anything, certain choices can add a feature while sacrificing another. It's up to the user to utilize the information out there (and there's a lot) to figure out what works best for them.