Hendrik, these engines move a lot of oil at high RPM's, unfortunately in a design flaw, they didn't cater for enough oil return galleries, and as a result, the head tends to fill up with oil, and you get oil starvation around the crank area. The later gen 3 4AGE 16V's took this into consideration, and have an extra oil drain on the intake side right behind the #4 intake runner. They don't have this issue.
Spoke to my dad last night, and he agrees that the cure is to fit a restrictor in the block, to lower oil flow to the head. He did one just this week for someone who races one in Cape Town, it also burned a bearing... They used to even do it on the Ford kent engines he used when doing oval track racing...
Tyrie, I'll run it in at 3PSI, and then have it set on 15PSI, if it lasts a few runs at that boost, I'll have it upped...
But there is a saying, and I think I saw it on this site, which goes, "When in doubt run more boost"...*hehehe*
EDIT: Hendrik, I saw that advertisement, and I'll give em a call. Fortunately my dad has many moons of experience in this kind of thing, and he wouldn't allow me to fit bearings that won't last...