Re: Barrel Life
There are a lot of factors in barrel life. Probably the first thing to do is establish expectations. What is adequate accuracy and why? If you're in competition your needs are different than if you're getting a beater .30-30 to shoot a deer a year with.
For hunting accuracy, I'd expect a "barrel burner" like an ultramag, STW, etc to exceed 2000 rounds useful life, '06 to be up around 4000, .223 in that ballpark, .30-30 ... if you wear out a .30-30 from hunting, you're doing a lot of "extracurricular" hunting! IMHO most "wear" in hunting rifles is from improper maintenance, not shooting.
Quality, hardness, durability of the barrel steel. Of course, the better the steel is for longevity, the harder it's going to be to machine precisely, so good barrels are expensive.
How are you treating your barrel? Don't let it get too hot to comfortably put you hand on and keep it there. Hot steel erodes faster than cold steel. Use a bore guide and one piece cleaning rod to minimize throat wear from cleaning. Use a solvent that is appropriate for the kind of steel you've got. Don't let the barrel get overly fouled between cleanings or you have to do harsh things to get it clean which shorten barrel life. Avoid harsh solvents .. better to use a mild solvent and let it soak longer.
I've used moly in a couple rifles. Even with rough factory barrels where it doesn't help fouling all that much, it does protect the throat from flame cutting and extend barrel life that way. On the other hand, it's a little bit of a pain 'cause you have to clean differently, the crap rubs off in your pocket, etc. It may or may not be worthwhile, that's a personal choice.
For competition, I've seen people change barrels on .243 class rifles at 1500 rounds or less because that quarter MOA their groups opened up are enough to make the difference between 1st and 5th place. Milder cartridges like the PPCs can go 3000-5000 rounds. When moly first hit public awareness one BR shooter I conversed with put over 10,000 rounds though his 6ppc competition rifle and couldn't measure any change in accuracy.
I shot moly in a .220 Swift. Sold it with 2000+ rounds though it. The new owner called to see why I sold it 'cause, via borescope, he figured it'd only had less than 200 shots through it looking at throat wear.
For the most part, for a game hunting gun, you don't need to worry about barrel life. With proper care it'll be measured in generations. If you use it for other things like a lot of offseason practice or varminting then it can become an issue.
Flex is for people who don't have lockers.