Just curious, what is it you hope to do with 20 fpe that couldn't be done with 16 fpe? And why alloy pellets? They are usually lighter. Energy transfer will be higher with a heavier pellet, and they will hold that energy better downrange due to higher BC. Trajectories will not be much different, if at all, once both are zeroed for the same distance.
You might look at the HW97K in .20 caliber. Pellets available in the same weights as .22, but with higher BC for better trajectory, better energy retention, and better penetration on game. I used .20 caliber for hunting for many years, and penetration was always impressive. Even at 16 fpe velocity will be over 700 fps, and once zeroed at 35 yards POI will be within 0.5" from 10 to 40 yards, perfect for the squirrel hunting I still do occasionally.