In my experience - even tho the A/F might be right on a wideband - your EGT's may be too high or too low. I saw 900 C + on my DSM even with the A/F right around 12 - 12.5 :1 on the dyno. I know for a fact that 900 + is not going to last too long. Hi EGT's could be due to several reasons. Here are 2 that are most commonly found on turbo cars.

1. too much overlap between intake and exhaust cams
2. Backflow from exhaust manifold into the combustion chamber - reversion) - usually if the A/R of the exhaust side is too small compared to the compressor side leading to too much back pressure.
3. ECU retarding timing to compensate for high knock count. (typical for turbo cars)

So you see even tho you might be seeing A/f's that seem safe sometimes its not the ideal tuning due to high EGT's. Thats the reason you must monitor EGT's.

thanks

Harry