I don't think they have to trade Iggy -- unless they want to get younger and shed his contract. They have nobody to backup at SG right now (unless you count 6 foot nothing Lou Williams) and Turner would probably be the best play maker on the team right away so he'd be their backup PG as well. Iggy is fine at SG or SF and he'll play minutes at both. They could go big with Turner, Iggy, Young and two of their bigs but probably their best starting 5 is Holiday, Turner, Igoudala, Brand, and umm, Hawes.
They really shouldn't give up on Brand as a starter just yet because he's untradeable, but even so I think Speights will be solid at PF. They need a center now more than anything else.