The weight really doesn't have anything to do with the distance a bullet is capable of. In the 168 class I've used the SMK, Nosler CC, and Hornady BTHP and Amax. In 155 class I've used the Scenar, Amax, and Berger. All of the 155's I've used out performed all of the 168's in supersonic distance, drop, and drift. IMO the 155 Scenar is one of the best long range bullets for the 308, and the best I have used to date. I'm talking real world use, not what it looks like in a ballistic computer. The Scenar gets way out there accurately and isn't finnicky at all to load for. You can jam it in the lands or jump it a mile, I didn't have that same experience with the Berger 155 or the Amax.
If anything is able to surpass the 155 Scenar I think it will be the Hornady 178gr BTHP or the Berger 185gr Juggernaut. I'm getting ready to experiment with the Juggernaut and I will be trying the 178gr BTHP once they are available again. The 175gr Amax and SMK are great bullets too but my experience has been the 155 Scenar typically equals the wind drift, has less drop, and stays super sonic longer.
Thats my .02.