in my 308's and 30-06 ive shot 150 grain factory loads for years, i dont know why but when I began reloading I began using 165 grain bullets. but have been thinking about going back to 150 grainers in a couple of my 308's. i guess the 165 will hold onto its kinetic energy longer at longer ranges then a 150 will, which is probably why i chose 165's when i started reloading. 150's will shoot a tad flatter and honestly might perform (mushroom) a little better on deer size game since the sectional density is somewhat less. but either will kill game just fine. you should buy a box of each and just see which your gun likes better. honestly it comes down to personal preferance anyway.