Don't think of it as higher margin on Comex. More like the margins on CBOT are lower as an incentive to trade with much lower liquidity. I prefer to pay up for the liquidity.
i just looked at the margin sheets and yeah comex 6075 initial and 4500 spec. cbot is 4050 initial and 3000 spec.
The CBOT may have greatly reduced exchange fees as an incentive to trade their contracts. If you expect to generate a lot of trades, it may be a better way to go.
This varies from broker to broker, but on IB the Silver margin requirements (large contract) for the eCBOT are 20% higher than for the NYMEX (Comex). Currently for ZI (5000 oz) on eCBOT: Intraday Initial -- 8,100 Overnight Maintenance -- 6,000 Currently for SI (5000 oz) on NYMEX: Intraday Initial -- 6,750 Overnight Maintenance -- 5,000 And as far as liquidity they're not even in the same ballpark, the SI blows away the ZI by many multiples.
From what I recall the contracts are 80% fungible from a cbot stand point. There are four silver contracts and I think you should have them all on the screen, similar to how equity traders have arca, island etc on their screen. Just so I don't get accused of anything I have research extensively silver trading but have yet to make a trade