Oneounce, my friend, I'd not sure I understand your propensity to download your guns. Next, I suppose you'll be suggesting 3/8 or 7/16-oz loads in the .410-bore. There is an optimum load per gauge (shot column diameter to length ratio). That's why there are so many different gauges. Our forefathers learned that pouring various loads down the muzzle of their big bore wasn't as effective as having guns with different bores. It's my experience, with 1,200fps loads, a 20-ga shooting 7/8-oz hits targets a lot harder than a 12-ga downloaded to 7/8-oz. The 20-ga is more efficient at 7/8-oz. As the officials keep reducing the loads used in international competition, I'm surprised that there hasn't been a change to 20-ga int'l comp guns.
Just the other day, Slugo was asking about the .410 vs. the 28. If he's really interested in shooting 3/4-oz loads, then a 28-ga gun may loom large in his future. Around here, many experienced shooters prefer 28s over 20s for doves.
I've known several shooters who do better with a 20-ga than a 12-ga, and it usually has to do with recoil/flinching. It doesn't happen so much with trap shooters because they shot only 12-ga, it happens a lot more with those who compete with the smaller guns. The typical Skeet competitor will practice with his .410 -- it's cheaper and if you can hit 'em with the .410, then other guns will take care of themselves (supposedly). For those of you with little experience shooting the .410, rest assured, it's very different than the 12-ga. After becoming acclimated to the little gun, going back to the 12-ga can be a rude awakening. For some shooters the difference between the guns is just too much. And, as my friend BigJimP mentioned, the 12-ga becomes a mental thing. My solution was to get a recoil reducing stock. It has an air unit so I can adjust the pressure so each gauge kicks the same. One of my teammates got 12-ga-psycho so bad that he chose to shoot his 20-ga in the 12-ga events. Eventually he decided to get a 12-ga Beretta gas gun. Like many others, I prefer the same gun in all gauges.