..but can guess what they'd aproximately do on co2 with a stock Disco. If you've modded it a bit, would expect a little bit more speed.
14.3gr. pellets (depending on which ones) run about 645fps on co2 during warm weather (over 80degrees) and earn about 13.2 foot pounds.
The heavier pellets will earn a bit more energy, but will be doing slower. to get to 14.5 foot pounds, those 18.2gr. pellets would be moving at about 600fps. To get to 15.7 foot pounds, the 28.4gr. pellets would be moving at about 500fps.
Really don't think you'll see quite that much energy jump from going with the heavy weights...sill see some, but would expect those 28.4's to be running closer to 490fps (15 foot pounds).