Re: edge or 338 ultra ai?
.338 RUM is very difficult to find at this point in time, .300 RUM by comparison pretty easy.
I have a 26" barrel on my .338 RUM. I don't know that it's true that more folks set them up this way, or that a higher percent of "Edges" are 30" tubes. I suspect that this is so.
I would guess from my experience, the shooters that are interested in the "Edge", are looking for every FPS advantage they can find. They want to stretch out how far their bullet remains supersonic, and get the most expansion possible at distance. A heavier barrel also enhances their ability to hit distant targets. At least in my group of friends this is the trend.
My standard .338 RUM is set up as a more traditional general use style rifle, it maintains portability, but is chambered for cartridge that can stretch a bit.
At the time I was thinking, factory rounds available, component availability would favor the standard chambering. If I was choosing now I would go with the "Edge". I have days when I consider having mine rechambered.