Flatter trajectories on iron sights I get, but speed doesn't automatically equal more energy AT the target, I will not go into specifics, but pick a cartridge, plug in the weight, velocity, and bc of the bullet into a ballistic program. Start with something small (like your 125) and then bounce up to 150 and 180 (even 200 gr for giggles). According to your statement of relying on speed for energy, you're correct up to a point.....the muzzle energy is NOT what you're counting on at 1-200 yds if you want "power" if that were the case, my .300win mag with a 110 gr screaming velocities would knock down a deer hundreds of yds farther than my 180s that are considerably slower and that is just not the case.....your bullet choice should be just fine, I'm just worried about the velocity energy misconception. In my .243 and 85 gr is deer capable and flat and fast outta the gate, but for shots over 250 I load 95 and 100 gr for bigger "thumps", and they start their run slower by 200+fps.
Sierra offers a 135 HP varmint bullet