The 308 has slightly less MV than the 30-06 or 270 so with the same bullet you would have slightly more flight time resulting in more wind drift and of course more drop but with almost any bullet you should have plenty of energy left for deer size game. Of course if you go with a lighter bullet of say 150 or 130 grains it would give you higher MV which would help.
Either way, practice a lot and watch the wind.
Going with a lighter bullet is going to make the 308 LESS effective at distance, not more effective. Flight time is a consideration, but the difference in flight time between lighter, faster bullets and slower, heavier, yet higher-BC bullets becomes irrelevant at ranges beyond 400 yards, and the higher BC bullet is going to be better at holding onto velocity and energy, as well as being more predictable in variable wind. Going light and fast has an outer limit of benefit, and it is generally about 500 yards, even with the biggest of big boomers, like the Lazzeroni cartridges.
