The WRX is now running much more smoothly with no CELs. While there is still more tune tweaking to be done, the initial results are promising.
I may have lost 100 - 200 rpms of spool, but the upper end of the powerband seems radically transformed. I am not used to seeing the tach climb as fast as it now does. It will take some time to evaluate the the overall feel as the tune improves.
Once the tune gets dialed closer to the ideals the spool up may yet increase. I'm still going over the logs along with my tuner. There is now ample headroom for the injectors.