The most accurate/Best sabot for your Omega is the one that works the best. Only way to figure that out is shoot it with a variety of sabots. But, that's not so easy until you figure out what size of bullet you would like to use.
Example meaning diameter.
.400
.451
.452
.458
Those are the most common above. Which all will usually require a different sabot.
I will take a guess with a .452 250grn XTP/SST the short black harvester sabot would be a pretty good choice.