Batllerifle: tests have shown that accuracy out to 300m is just about the same (less than 1" difference in groups) between round nose and spire point boat tails. With this in mind I would recommend any factory 150, 168 or 180 gn load.
As far as 'flat' is concerned, the midrange trajectory on any of the 3 bullet weights mentioned would be about the same. If you are zeroed at 100m, you will be about 2-3" low at 200 and about 9" low at 300. If you zero at 200, you hit a bit higher at 300 and hit about 1.5" high at 100. If you have your rifle sighted in for a specified distance you can figure your trajectory out to farther distances and yes, factory 06 loads will take large animals (Elk, Moose) out beyond 300m.
You may get slightly flatter trajectories with 'light magnum' loads but they are heftier on the shoulder.
I would recommend the 165-8 gn slug as a midpoint twixt the 150 and 180 gn bullets but that is your preference and it depends on the game you are after. Whitetail don't need a 165 or 180 gn bullet, but the lighterweight bullets in 30 calibers create a lot of meat damage which is why I prefer the heavier 180s.
The concept of 'flatter shooting' is fairly moot with standard pressure loadings and regardless of caliber, most standard pressure loads have about the same trajectory and all within an inch or so of each other. JMHO. Mikey.