The stated 75 MOA on the Leupold VX-3HD is approximate, and actual click count can vary slightly due to internal tolerances in the erector system. If you’re missing that much travel, it’s best to send it to Leupold so they can check and recalibrate it.
Geometry Dash
I’d expect you to see something in the 1,000–1,050 fps range from a 10.5" barrel with that load, but always work up carefully since every barrel can chrono a bit differently. Pokerogue
A braked 300 Wby may feel somewhat like a non-braked 7mm Mag, though the actual experience can vary depending on the brake and rifle setup. It should be much more manageable than an unbraked 300 Wby, but the muzzle blast and noise could still be intense, especially without ear protection.
Retro...
If aesthetics are your priority and you don't mind potential maintenance, the 4140 with Cerakote should be fine, but if corrosion resistance is crucial, the 416 SS version is the better option.
Slope Game