122.75, as everyone has said - is pretty much it for "legal" A/A freqs. The problem is if you're doing formation work with a group and there is an active "training area" nearby, there is no way you're going to be able to cleanly do your formation work. Because that "practice area" freq is going to be busy.
I do a lot of formation stuff here locally, usually as a 2 or 4-ship lead. We have several freqs that we use for interflight "Company" or "tactical" usage. We use them because we know they are clear freqs not in use in the area. And that's mainly from trial and error by just listening and seeing if anyone is there or not.
Published transoceanic freqs are usually pretty good to use, especially if you are well away from the coasts. Again, NOT LEGAL. But workable in a pinch.
Buy yeah, I would definitely stay away from 122.7, 122.8 and 122.9 - as those are common unicom freqs at untowered airports.