Jerry i'm not saying your wrong here but there are several (4 off hand) twin turbo vehicles running the DSP and are in the 1000 RWHP range.... more than a couple of dozen running with direct ported nitrous (900RWHP range) and of course you standard S/C applications (800-850 RWHP range)... All these are using DSP with a single A/F wide band. Now almost all of these guys are running ungraded fuel systems (Boost a pump, Fore, AN lines and larger fuel rails, ETC..) But these guys run their cars very hard with no issues with leanness. To me if you wanted to be safe you could run another AF wide band on the over side to monitor the bank.
Jason