On the Lapua bullet,I have never used them,can't say,other than they have a good reputation.My point in replying..BC can seem like an obvious advantage.It has been my experience that long,skinny ogive bullets may shoot great in your rifle,but maybe not.I'd suggest buy and try 100 maybe.
Sierra makes a Palma match 155 gr bullet with a great BC,but I could not get it to shoot out of a 2.800 mag length load in an AR.Not a bad bullet,just not a good application.The old 155 gr Palma,now the 155 gr Matchking,shoots good with less BC.
Another factor,as the bullet gets a long ogive,and a boat tail,in a light bullet,there is not a very long length of cylindrical diameter to ride the bore.
That can make it harder to get results.I typically use a boat tail with heavy bullets,but in a lighter bullet at closer ranges,a flat base may shoot better.
Twist?A 1 in 12,1 in 11,1 in 10,all might be possible.That may help select bullet weight.
Really,if 300 meters is going to be the limit for a place to shoot,some things diminish in importance,IMO.A .430 BC bullet vs a .490 BC bullet will matter some at 300,but not very much.Same with 2750 fps vs 2625.Yes,it helps some,but you certainly may find longer barrel life and perhaps better accuracy at the lower velocity.
I can't give a recommendation between N-135 and N-140 for you.Just choose and try,but,for myself,I think I would prefer 140 for the flexibility with a possible heavier bullet choice.