Updates after 1500km on the current oil: no visible oil consumption, dipstick at full mark, knock on wood.
After a session with a paint marker and very careful adjustment of the Rs. 1000 Chinese boost controller, I've finally managed to get some very nice early spool at 7 psi at partial throttle, and 12 psi maximum before the wastegate opens. The car feels much nicer to drive. Finally, this is what the wastegate would have performed like when new.
But, I wish I could do something about that damn fuel cut at 12.8 psi! I'm juuust at the point where it overboosts and cuts fuel if I smash the throttle while the engine is below 3k RPM. It's a great safety feature, but annoying in this context.
The silver lining is that I apply the throttle much more judiciously now, since the turbo is very eager to spool at the slightest touch.
The only solution is a more precise single-stage boost controller that doesn't use a ball and spring. They're not as costly as an ECU upgrade, but the spectacular performance of the rupee makes it difficult to justify the purchase.
Of course, changing the ECU to a Suzuki N1 or N2 would be exciting, since both of them remove the fuel cut and raise the rev limit, but they're not available in Pakistan. When one does eventually turn up at a Japanese auction site, the price is usually around ¥100,000 - $700 in today's money, excluding shipping and duties.
An interesting observation is what I suspect is the limit of the SOHC when driving hard. @Xulfiqar called this earlier:
I never exceed 5000rpm, but after a gear change, the turbo spools so much faster than the engine inhales air that the BOV is open for a second or two until the pressure difference favors the engine and closes the BOV. Is this a maladjusted BOV or just the engine not sucking in enough air?
I will say, the reference line to the BOV is quite long - the longest vacuum line in the entire car.