an AFR of 13 would be considered quite lean for any positive boost pressure. That would explain the high EGT. I would aim for a minimum of 12.5:1 but would prefer 12:1 or slightly richer, approaching high 11's
There are a couple of wideband options. The bosch and NGK EUGO sensors. Does anyone know what the differences are?
A useful link is http://www.techedge.com.au/vehicle/wbo2/default.htm
I purchased a kit form here, and it seems to work well. Although I would like a little more info on the sensors...