This is all excellent information. I am currently in a rebuild of my 96xxx mile '05 OBXT after a burnt exhaust valve on cyl 2. After MUCH consideration I decide against also redoing the block with forged pistons. It is a gamble especially with my plans for this "daily driver", but if I loose a cylinder again, I will just have to yank the engine out and fix it. Fortunately these subarus are very simple to work on.
With respect to being at stoich under boost, with the factory tune my car did
remain closed loop/14.7AFR until around 3-4psi. The "stage 1" tune I am running now, based off a tune posted on romraider's forum, turns off the factory counters for the CL/OL fueling switch and now runs OL much sooner. It's actually off the scale rich on my AEM WBO2 (<11:1) which IMHO is better than high 14's under boost
The pistons have major carbon build up even with running two tanks of BG44K and seafoam through it before the tear down.