Gurn,
Quick answer, Yes, the Elliminator III will work on the 450.
Long answer, what is you true efffective and optimal range with the 450? Will you have a bench to shoot from or will you be off hand or leaning on the side of a blind with little support? If you will be on a bench, you effective range can be 300 yards. If not, I doubt your ethical range would exceed 200 yards. With the ballistics of the 450, your drop is massive from 250 yards out (depending on your zero), any small miscalculation or motion by the shooter will be grossly magnificated down range.
Also, will you be walking and shooting with this gun? If so, as much as I love the Elliminator, it is not necessarly the best choice for quick snap shots. A2x7 or 3x9 might be your best choice. Looking at the Ballistics for your round, you could adjust your zero to your optimal terminal point.
I have attached two separate drop charts for the standard Hornady 250gr load with velicity of 2200 from the muzzle. If 90 percent of your shots would be 150 to 200 I would recommend at zero of 150. If 200 to 250, mabe a zero of 200. You could zero at 250 but then your close shots would be 9" high and 300 would be 10" low.
For drops of this magnitude, I personally feel the effective range of this gun in most hunnting applications is 200 yards. While you still have ample energy (1275 FPE) at 200, your velocity has dropped to 1515 fps. At 250 your energy is down to 1052 and velocity 1376. At 300 it is 875 fpe and 1255 fps. I personally don't feel ethical about shooting at deer sized game with energy below 1000fpe, even though less can kill, it is my personal belief not to do so. Also, I feel shooting long range takes ethics. Just because you "might" hit the deer or target animal does not mean you should try. I have seen too many animals in the woods that have been wounded by inaccurate shots with high powered rifles at normal range for a menagerie of reasons and these gun are designed for the ranges shot.
So, if you plan to streatch this gun out, dont beleive the paper number. Learn it, shoot it and be able to duplicate it before you dope the scope and fire one off at an animal. That goes for any gun, any scope, and live target. We owe that to our sport and to our game.
Happy shooting.