Barrel life's something that's measured with a rubber ruler. By that, I mean that we all have a limit that our barrel's accuracy is considered not good enough. A benchrester will rebarrel when his 100-yard groups start averaging in the 2's instead of the 1's (2/10ths inch instead of 1/10th). A hunter wants a new barrel when his .30-06 no longer averages under 1 inch at 100 yards. A soldier gets a new barrel (or rifle) when it no longer shoots 2 inches or better at 100 yards. The benchrester gets 3000 rounds with his 22 and 24 caliber PPC ammo. Hunters using a .30-06 get 6000 rounds. Service rifle shooters with M1's and M14's as well as M16's get 9000 to 10000 rounds of barrel life.
Regarding rapid fire barrel life compared to slow fire, consider the following, which I think is a fair comparison.
Sierra Bullets shoots 30 caliber bullets 180-grains and less from .308 Win. cases testing them for accuracy. They shoot 10 shot groups from their rail gun in a minute or two; one shot every 10 to 15 seconds or so. This is repeated about every 20 minutes during a production run of bullets that are made at a rate of 90 per minute. That test barrel shoots match bullets into 1/2 inch average groups in their 200 yard indoor range. It's tested every several hundred rounds with "standard" bullets from a control lot. When those standards start shooting upwards of 3/4 inch average, the barrel's considered worn out. That happens at about 3000 rounds.
Palma rifles chambered for the .308 Win are fired once a minute for 17 to 20 shot strings. The good ones shoot under 3/4 MOA at long range starting out with a good barrel. When they begin shooting over 1 MOA, they're considered to be worn out. That happens at about 3000 rounds.
NRA match rifles in .308 Win have 1/3 of their barrel life shooting rapid fire matches, two 10-shot strings in 60 or 70 seconds each 10 minutes apart. 2/3rds of their life is slow fire shooting 1 shot per minute (or a bit less) in 10 or 20 shot strings. The good ones shoot under 1/2 MOA through 600 yards but get rebarreled when accuracy drops off by 50%. That happens at the same number as the others, about 3000 rounds of barrel life.
Barrel maker Boots Obermeyer has often stated that rapid fire does not wear out barrels any faster than slow fire when normal max pressure loads are used. It's those hot, over maximum, loads that cause the shorter barrel life. And some powders are more erosive than others, too.
Here's a link to a barrel life calculator:
http://www.accurateshooter.com/technical-articles/excel-formula-predicts-useful-barrel-life/