I have two Omegas and both are older rifles from around 2002-2003 and they are not particularly tight bored.
The one rifle shoots 100 grns of 777 and a smooth green Harvester Sabot with the 300 grn .430 XTP. Three shots under an inch at 100 and the bullet does very well on deer too. I have never shot Blackhorn209 in this rifle because I was waiting until my 777 was used up.
This rifle shoots the .452/300 grn XTP with 777 well too, but the .430/300 grn XTP does better.
The second Omega shoots the .452 300 grn XTP in a Crush Rib Harvester under an inch at 100 with 110 grains of Blackhorn209 and it chronographs at just a hair under 1900fps. This rifle did not shoot the .430/300 grn XTP very well when BH209 charges were 100+ grns.
I would recommend that if your rifle shoots the .452/250 well, try the .452/300 in the same sabot and see how it does. That is at least where I would start. But you'll have to try both the .430 and the .452 300 grn XTP's to know for sure--every rifle is different....