I own and use both on pretty much everything . With 180 gr bullets , there isn't much to choose between . With heavier bullets , like a 220 gr , the 308 loses ground . How important that is , I'm not sure . With newer bullet designs , a 180 gr will do all I need . If you're using old school cup and core bullets , the 220 gr round nose will penetrate a lot of flesh and bone . A friend of mine is a biologist in the North West Territories , most carry 30/06s loaded with traditional cup and core 220 gr RNs ( you don't see much high end ammo up north ) for protection against Polars , they work . Before anyone asks , most don't carry 375 H&H and similiar large game rifles because they're too heavy , expensive and , in the Arctic especially , hard to feed . On a related note , the majority of the Inuit guys I know still use Lee Enfields to shoot everything from Walrus and Polars down through Seals and Caribou . From a realistic standpoint , I'd lump the 303 Brit in with the 308 and the 06 , with shots under 200 yrds and similiar bullets. I've shot a fair number of animals with all three over the years , can't say I've seen much difference between any of them in the field .
AB