G-man,
I think you also need to consider the make and model in the mix and your personal experience with gauges other than 12g. Some guns may be very attractive to you but may be excessively heavy or light in the gauge you want it in, so if you're stuck on a make/model, the gauge may be a fallout of the other features you want. The most important thing is gun fit, then other things like gauge, weight, etc.. If you know your dimensions, great! If not, get a fitting.
There's no question, a 12g has the capability of taking more game due to the ability to carry a heavier payload. I have a pile of them. But, an upland gun is not all about the payload. It's also about weight, fit (with hunting clothing), versatility, and what makes you feel good.
So, for an upland gun, my preference is the 20g over the 12g in most situations. Last yr in SoDak, I shot only 20g guns and never reached for one of the 12g guns in my truck. I never felt I could have made a shot better with a 12g on that hunt.
For your uses, I'd look for a 6 to 6 1/4 lb 20g capable of handling modern 2 3/4" ammo. If you lean toward the 12g, I'd look for a 6 1/2 - 6 3/4 lb gun capable of handling modern 2 3/4" ammo.
