I think it's safe to say (according to 2ndGenDsm, JDMEvo, and myself), that it's not really worth pushing much more, (if any), boost at all.

You may get a slight bit of performance by raising it a couple psi at most. That's basically what the stock guys do when they do the BCS Restriction Removal (like I did). Quite frankly, I didn't really feel too much of a change either. You may get a little more romp in your acceleration at most, but nothing to take home about.

Just start saving up for a 14b or larger and call it a day. 14b's can be had for cheap and give a significant improvement in performance, even with mild tuning.