I normally load the 175 gr Sierra MK but am trying out the 175 gr Berger to see if it offers any improvement.
All Palma shooters and some LR and F-class load the 155 gr Sierra or Scenar, partly because that is the maximum weight allowed in Palma competition and partly because the bullets have high ballistic coefficients and are still light enough to give high velocity. Ususal loads are at the utter maximum for .308.
The 168 gr bullets are not usually adequate for 1000 yards. I have seen one guy doing well with them, but I have seen others not. Some ranges won't even allow them to be shot at 1000 yards because unless loaded very hot, they go subsonic about 900 yards, lose stability, and are considered hazardous.
A few people use heavy bullets like 190 gr SMK or Berger. They seem popular in Australia.
I am a casual occasional recreational Long Range shooter.
There is a lot of good information at
http://www.long-range.com/forums/