I am not sure why anyone would want to trade QQQ/SPY etc.
The eminis offer round the clock trading, little slippage, lower commission and very beneficial tax treatment. The tax benefits of trading eminis vs stocks usually pay all the commissions for the year.
You sound like a experienced trader, but for novice traders its not a good idea to start trading futures until you have a proven trading record. If a trade 'gets away' from you it can cause substantial dent in your account in a short period of time.
Good luck trading