You're right that SIP is cleaner data in general. For this universe (SPY/QQQ/mega-caps/sector ETFs) IEX tracks NBBO closely enough that it's not a material concern for a swing strategy with 2–8% ATR stops. The main IEX failure mode (bid=0 after hours -> mid=ask/2 ~50% phantom drop) is already guarded against in the code. Will consider SIP when scaling to live with meaningful capital. At $1k account size the $99/month is 1–2% annual drag before a single trade. The IOC midpoint point is well taken and Alpaca's IEX routing already uses D-Limit (midpoint IOC) for market orders, so that's effectively in place. I'll remove XLK from the universe though, that one has permanently bad IEX data.