If you want the hottest factory ammo, the Buffalo Bore 300gr at 2350fps would be my first choice, sighted in about 4" high at 100yds, it's dead on at 200yds and 17" low at 300yds with over 1300lbs energy remaining. Their velocities are from 22" barrels, so the calculated trajectory should be fairly close, but you'd want to shoot it at 200yds/300yds to confirm it.
Tim
http://www.buffalobore.com/ammunition/default.htm#4570Trajectory for Custom .458 Speer 300gr Unicore at 2350 Feet per Second At an Elevation Angle of: 0 degrees
Ballistic Coefficients of: 0.206 0.206 0.206 0.206 0.206
Velocity Boundaries (Feet per Second) of: 2350 2350 2350 2350
Wind Direction is: 0.0 o'clock and a Wind Velocity of: 0.0 Miles per hour
Wind Components are (Miles per Hour): DownRange: 0.0 Cross Range: 0.0 Vertical: 0.0
Altitude: 0 Feet with a Standard Atmospheric Model.
Temperature: 59 F
Data Printed in English Units
Range Velocity Energy Momentum Drop Bullet Path Wind Drift Time of Flight
(Yards) (Ft/Sec) (Ft/Lbs) (Lb-Sec) (inches) (inches) (inches) (Seconds)
0 2350.0 3678.1 3.13 0.0 -1.5 0.0 0.000000000
25 2249.4 3370.0 3.00 -0.2 0.52 0.0 0.032620840
50 2151.2 3082.2 2.87 -0.83 2.1 0.0 0.066715505
75 2055.5 2813.9 2.74 -1.94 3.22 0.0 0.102382600
100 1962.3 2564.6 2.61 -3.55 3.83 0.0 0.139727445
125 1871.7 2333.4 2.49 -5.73 3.86 0.0 0.178862588
150 1784.0 2119.7 2.38 -8.53 3.28 0.0 0.219907455
175 1699.3 1923.1 2.26 -12.02 2.02 0.0 0.262985995
200 1617.8 1743.2 2.15 -16.25 0.0 0.0 0.308223922
225 1539.9 1579.2 2.05 -21.32 -2.85 0.0 0.355746921
250 1465.7 1430.9 1.95 -27.31 -6.61 0.0 0.405675969
275 1395.8 1297.6 1.86 -34.3 -11.39 0.0 0.458120303
300 1330.4 1178.8 1.77 -42.41 -17.28 0.0 0.513170980