Mike, gen 5 has quite a few upgrades. The biggest are better trigger, match grade barrel, ambidextrous slide release, no finger grooves and it comes with additional back straps to fit the hand better. It also has front slide serrations to pull the slide back easier, mag release is slightly bigger, dual recoil springs, and lastly Some internal changes with a more reliable trigger spring, new drop safety plunger, and a redesigned firing pin. The gen 5 was made to be more comfortable, accurate and reliable. Believe it's definitely worth the few extra bucks. Hope this helps.

What I like about the gen 5 is definitely the backstrap swapping! Nice beaver tail to tuck up against! And yes, the marksman barrel is an improvement along with a crisper trigger pull/reset.

Hi Mike, Definitely Gen 5, it’s much more refined. Trigger is way better, grip is better, backstrap capability, front serrations, better barrel. It feels better in my larger hands (I have the Gen 5 Glock 20 in 10mm. -- youtube.com/watch?v=SAnlmtRPM0k