I have to agree with Cayugad. Some of the 1:48 twist barrels can be mighty finincky when it comes to saboted bullets. If your conicals shoot good you might want to consider staying with them. You can try 275 or 320 gr Maxihunters or 370 gr Maxiballs.
But if your considering going with the sabots I'd stay with the heavier ones (300 gr). Cayugad mentioned the 300 gr .451" XTP. You can also go with the 300 gr .429 XTP and green Harvester CR sabots.