I agree, if your goal is 2.5 moa than you are likely to be able to achieve that with some care...and some occasional fliers.
Those in my picture above are 0.458 sabots and 150grain SST's.
I also am only in the 3k fps area and you are likely 1k or more above that. I do also shoot 150 8mm Game King bullets from my 0.505 barrel at well under 1 moa.
I originally shot sabots based on those in your picture, actually those from Beastwerks, but accuracy was not what I wanted for deer hunting. I began searching the web for sabot designs and found that much of the dispersion in military rounds was either from a lack of support in the barrel ( balloting), which should not be an issue with your sabots, or inconsistent sabot separation including various amounts of contact with the sabot during separation.
Out of curiosity, do you get 50 cal holes or 30 cal holes in your target? IF you get 30 caliber holes, I might suggest that you epoxy or super glue the bullet into a few sabots to ensure that they do NOT separate! If these bullets are substantially more accurate then sabot separation IS an issue!
When testing sabot designs I do not slit the sabot petals for the first few shots to make sure that they are leaving the rifle in a stabilized manner. Only after I am sure that I have nice clean 50 cal round holes do I make the sabots of the discarding type.
edge.