Yep.. the Extreme Elite is a sabot/bullet.... not a conical.
If Cecil says the Hawkens shoots the 300 gr well, I believe him. He has helped alot of shooters find the right loads for their MLs.
If you want a nice conical from PR Bullet, get the Keith Nose. All PR conical/bullets come unlubed -- so that may change your mind about purchasing them. Some ML users just don't want the mess associated with lubing their own bullets. If that's the case, then try some REAL Bullets from Black Jack Hill. Just Google 'Black Jack Hill" and order some of his soft lead 320 gr. REAL conicals.
I know poster Lonewolf has ordered from Hill. He may help you a little more with that.