Water temp too high / Oil pressure too low

[Hatzenbach]

I recently upgraded to a 996 cluster and am now able to watch my oil pressure when I drive on the track
At my last two trackdays (both with 90+ degrees ambient temperature) I noticed that after about lap #3 my oil pressure went down dramatically:
I usually have the gauge above "4" in normal driving conditions when the RPM are higher than 4k. On the track I noticed that the oil pressure went below "2", even at 6k+ RPM
This has nothing to do with oil starvation as I could repeat this after I was back in the pits (so no high g-forces etc, the car was standing still).
The water temp went up to around 215 ~ 220
I noticed that there is a direct correlation between high water temp and low oil pressure (duh)

This happens only on the track and with high ambient temperatures
The car does not overheat or display low oil pressure when normally driven

I have a deep sump kit and I don't think that an accusump would help here as this is an ongoing issue, not just a spike when cornering at high G

The radiator fan kicks in and the radiators are free of debris (I have wire mesh in front)
I also switched from 15W50 to 10W40 with no improvement

Any good ideas as where to look/start?