As much as I love the 308 I will concede that there are better options for match calibers such as the 260, 6.5X284, 284 etc.....Dont get me wrong, you can wring a pretty impressive 1000 yard match load with a superior BC out of a 308 but you will pay the price for it and that is recoil. The recoil in and of itself is not bad in general compared to other calibers but for 20+ shot stings you will ge recoil fatique. They also do NOT allow muzzle brakes
in competition so you should be looking at a shoulder saver. The 260 for example will offer you a light weight 140-142 grain bullet with BC's ranging from .590-.620. these will fight the wind well and not tenderize your shoulder. The 308 will deliver a 208-210 grain bullet with BC's ranging from .620-.650 and will fight the wind only slightly better and tear your arms off after a long match.
That said, when you ask about the max effective range of the 308 with match ammo, it is going to depend on if you are talking animals or paper. For paper there are many loads that will reach the 1K mark no sweat. There are only a couple that will make 1300+ yards.
The 300WM is a great all around rifle but not for matches. For one the barrel will cook pretty fast when shooting strings of 20+ rounds during a course of fire and if you are not flinching by the end of the day, then by the start of day two you will be and you WILL get the crap kicked out of you. You can add a couple hundred yards for the 300WM over the 308 for effective match range.
For a guy just starting out the 308 is a great round. If you are not too concerned with the hype of BC's etc......the 308 can offer a new guy great possibilities. You can learn to shoot without breaking the bank, ammo is easy to find, the 155's are a great 1K load that wont beat you up, they are extremely accurate to build your confidence, good long barrel life so you can actually learn how to shoot etc.....
For the record, the 308 is my favorate cartridge. I shoot matches with it and I hunt with it. If I were going to get really serious about shooting alot of matches though I would look to a smaller caliber. From a hunting standpoint, it works just fine. My 308 opens a hole in the animal. Magnums open holes in mountains. I could care less about the hole in the mountain.
I hope that helps!