If the ammo cost isn't an issue and you're not trying to be competitive, go for it. A few people ran 308s in IPSC rifle last summer and while they were at a distinct disadvantage, they sure had fun.
The main issues were that the recoil slowed follow-up shots, and many were using 5 round mags rather than 50 Beowulf mags. 3X more mag changes has a huge impact on times. The M305s that were run are also slower with mag changes than AR10-type rifles.