Those "Speed" sabots would need the tail cut off. Those are more or less a gimmic. I did not think they made them anymore.
Powerbelts are not used by many here. They are way too expensive for what you are getting and are made by CVA so they push them.
If you want to save some money and still get a good load for your CVA, Pick up a pack of Harvester Black Crush rib sabots and a box of Hornady 300gn 45cal .452diameter XTP pistol bullets. Put that on top of 2 of your 777 pellets and see how it shoots. My nephew uses that combination in his CVA Wolf and it loves it. It is also a great Deer load for him. Buying your bullets and sabots in bulk (those XTPs would come 50 to a box and sabots are also 50 to a pack) is much cheaper then those Pre-Packaged offerings.
Pellets also are not used much here for several reasons. You are limited in load choice since you can't work up and down in 5gn increments. The boxes are not sealed so they can draw moisture, so don't plan to carry them from year to year. If you do, try vacuum packing them after your are done for the year unless you plan to shoot them up.