If it were me I would go with the krink. I believe it would be more reliable. I have no hard info the subject, but just looking at the mechanics of the two actions, the AK's gas piston system would be more reliable in my eyes. Heck, it seems like most guys that are building SBRs are going with gas piston set ups these days anyway to alleviate prior cycling problems common in shortend gas systems in the AR platform.
The krink was designed to operate with a short stroke gas piston and it does just that, and quite fine if I might say so myself. Also, Look at the Draco AK pistols. Again, short barrel, short stroke gas piston operating system that functions flawlessly. I have one and it eats everything I feed it. I have two other friends with Draco's that also function just fine as well. Thats 3 for 3 in favor of the krink/draco short stroke gas system.
Plus the 7.62x39 round will carry more ummph upon target impact as well as making a bigger hole for blood to escape the body quicker, which will result in a quicker death for the victim. Ammo is also ALOT cheaper so you can PRACTICE PRACTICE PRACTICE!
These are just my thoughs and opinions.....
Im sure the AR fans will begin my bashing shortly......
Biggest issue with a short barrel.........NOISE.....put your ear plugs in before you take it off safe! That and muzzle blast. You better be wearing tinted safety glasses at the range. Beachball sized muzzle blast is common. Look into a Noveske flash hider. Theyre supposed to be the cats meow for taming the blast.