I know that they are either anti-pump up and/or have a fast bleed rate. Have any of the mid-range->top-end turbo people upgraded or think about upgrading theirs and to which type?

doing. IIRC there had been an issse with the runners, no?
I THINK that this was one of the before mentioned weak spots with the motor.

quite a bit. The valves might unseat themselves at high rpm as the oil pressure increases.

When I rebuilt the engine, i installed a new one.

will check it every 35Kmiles, also the cam belt tensioner, that is another prob area.