if thats what you are looking for is the most bang for your buck in the velocity department in a model 20 nula then the 284 winchester and 6.5-284 should be your picks in the calibers your looking at....you could also consider the 25-284/6mm-284 for something different but i am thinking to get the most velocity in what calibers fit into the model 20 you would have to go with a 284 winchester based cartridge
