Sarasota; sachabr makes a good point. Size in mini will typically get filled by a pit local with a hand held Globex terminal after the pit has turned. Thus you're invariably giving up an edge. No big deal since size always must make a concession.(That's what makes markets move, eh). However a more distinct disadvantage for a size ES trader is commissions. I think I mentioned this to you on a previous thread, that you're going to be hard pressed to pay less per 5 ES then you would on 1 SP. 100 minis would probably cost about $100 more in juice then 20 SP. In addition the pit trades in dimes as opposed to the screens .25 allowing the rare fill on the inside. Granted it's apparent that at some point Globex will overtake the pit, but until then, trade size where YOU have the best advantage.