Derek, I also found this, also posted by Mr. Allen
I have tested a couple ABS carbon wrapped barrels in my 338 Allen Magnum and put them through some torture tests along with two all steel barrels, one from Lilja and one from Krieger. The ABS barrels both used Rock barrel sleeves. The test was to fire five, 10 shot strings. Shooting was done by shooting 10 shots as fast as possible. Let the barrel cool to the point I could just hold my hand on the barrel, repeat with 10 more rapid fire shots and continue to repeat until 50 rounds were down the barrel.
I did this with all four barrels, two ABS, one Lilja, one Krieger. After the test all barrels were pulled, cleaned and inspected for throat erosion and heat cracking. In the end, The ABS barrels had roughly 8 thou less throat erosion(throat length) then the Lilja barrels but they were identical, within +/- 1 thou of the Krieger. Heat cracking appeared to be nearly identical in all barrels.
He also stated in a post that he uses lilja barrels 10:1 on customers rifles.
I'm 16 "Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth." ~George Washington
"The only advantage a light rifle has is weight, all other advantages go to the heavy rifle."
~ JE Custom
Since it sounds like you will be shooting this 300 RUM quite a bit and weight isn't your #1 concern, I would think about doing a 30-32in. tube in a contour that would allow you to have the barrel set back and re-chambered when the time comes. In theory, it should/would give you a longer usable barrel.
Also, since you are going with a fairly longish barrel I wouldn't skimp on contour. I would use at least a Sendero or larger contour. The longer you go in length the bigger the contour needs to be.
Using a Lilja 28" number 8 contour fluted 3 groove on my custom 300rum, shooting 215 hybrids and I'm very happy with the accuracy I'm getting.
Have Lilja barrels on a 338rum and 300wm both are very accurate.