As Gary mentioned, for 300rwkw on a twin setup,you want the most efficient turbos you can find so you would either search for a set of HKS GT2510's, or for the newer option, GT-SS's.
Both will comfortably reach the power goal and its already a well known fact that for response, its hard to go past GT-SS's, especially at ~$3,000 for a complete kit (Half the cost of the proposed SST setup!)