Hi there. I have been running an ATS for while using to SPY to buy the S&P500 and SH to short it thru a margin account at Interactive Brokers. I am wondering how simply selling short SPY would be any different wrt. costs? I have no experience in using short selling on a margin account - is there anything I should be aware of? (The advantage would be that I could use the same model for other assets - i.e. silver or the deutsche bank commidity index (dbc) for which there do not exist a short fund.)
Futures are too leveraged for what I do. The exposure futures would give to the underlying is too big compared for the time horizon and the account size I have.