I'm leaning towards a piston gun for a number of reasons, and yes I do understand the arguments that it answers a nonexistent problem. The biggest reason comes back to when I was in the Rangers and we did a bit of shooting with the C-7. I was, shall we say, unimpressed with the degree of carbon buildup on the bolt and carrier, and very impressed by the difficulty required to clean it off. That cannot bode well for the longevity of the component parts subjected to that amount of heat, or from the corrosive effects of the carbon fouling and the subsequent efforts to remove it. The piston keeps this fouling up at the gas block, rather than on intricate moving parts of the bolt, carrier, and trigger group. I doubt if heat will become an issue with the way I intend to use the rifle, certainly not compared to a select fire rifle used by people who think the purpose of full auto fire is to empty magazines as quickly as possible. But there is a temperature component to my choice as well. A DGI action from what I understand requires a wet bolt to cycle reliably, where as the piston gun requires just a light skim of grease on the bolt rails. If this is indeed correct, and despite the availability of very good low temperature lubricants, for my purposes and considering the cold conditions this rifle might be subjected to, the piston might be a better mousetrap, particularly now that issues related to bolt tip, and a free floating forearm have been generally addressed and resolved. There comes a question as well as to the uniformity of the ammunition I might have access to. I wouldn't expect handloads to pose any cycling problem, but if tempted from time to time to purchase lots of non-Nato stamped milsurp ammo from off shore manufacturers, the gas piston action might be advantageous from a reliability standpoint, particularly considering the conditions I might use in.
Piston type actions have proven reliable under all conditions on earlier military auto rifles like the FAL, G-3, and the M-14, so its not like introduction of something that's unproven. The gas piston is simply a component that Eugene Stoner thought could be eliminated in a more modern approach to a fighting gun, and in California's climate, he was likely correct. I'm not so sure if it applies to the accessible arctic in mid-winter.
Still, the jury is out as to which gas system I eventually purchase, and the down side of the gas piston system is that it increases the cost of the rifle by about 30%! I can't ignore that either.