EJ207 heads are better than EJ205 heads. But, if your going to get the EJ257 heads I would go with those b/c of the AVCS. Also, I believe (someone correct me if I am wrong) there are some wiring issues to figure out w/EJ207 heads on an EJ257. Also, I would not go the hybrid route if you already have a STI/EJ257 longblock.
So, I agree w/Basco put the longblock in. I would also throw some forged pistons in there and even consider a mild cam upgrade (i.e. Kelford 264s or Tomei 252s) to help improve the top end, depending on what turbo you choose to run (smaller the turbo = smaller grind cam; larger the turbo = larger grind cam).