I dont own an Encore (i have a contender
), but i DO use all three cartridges your asking about. Personally if i was only going to own ONE of them id get the 7mm (i assume remington magnum), It shoots flatter then either of the others hits harder on both ends then the 06, and quite a bit less then the .300. Course I also think your looking at rounds that do best in 24" 26" and 28" barrels respectively. You DO have a broader selection of bullets for the .30s, If your shooting only hunting bullets (I hunt with bergers and Amaxs), then the advantages of the 7mm arnt as pronounced.