As you’ve gathered so far, the differences between Glock Gen 4 vs Glock Gen 3 are moderate. Nothing is changed internally or really all that substantially; the gun is pretty much the same except for some surface changes. That said, those surface changes may make a difference to you.
The stipling on the Gen 4 Glock pistols is a little more aggressive. You’ll get a bit more secure of a grip. Granted, some people don’t like that as much; some pistols feel almost like the gun could double as a low-grade rasp and that’s annoying. (1911 grips, am I right?) However, some prefer the added traction, especially when shooting with gloves.
Another feature that the Glock Gen 3 guns lack is the modular backstraps. It either fits you or it doesn’t and there’s not much to help it if that’s the case short of an aftermarket frame. The Gen 4, on the other hand, has several sizes of backstrap that can be easily swapped in for a better fit. That’s a plus if the standard pistol doesn’t have the best fit out of the gate.
There is also the reversible magazine catch for lefties, which is a plus. The dual recoil spring…may extend the service life of the spring itself, but whether it really reduces felt recoil at all is quite subjective. You may think so, you may not.
You’ll have to get out and handle both. Shoot both if possible. That will tell you which to get. The thing about Glock Gen 3 vs Glock Gen 4 is the guns are almost identical; it’s just that the latter has a few more bits of kit than the latter, and at that not a heck of a lot. Whether they matter enough to spend a little more for the Gen 4…is up to you.
Source: Alien Gear Holsters