Thanks amg6975 - was at the track this past week and yes, there is clearly a restriction in the factory cooler. I see that some have removed the factory restrictor (or whatever is underneath that metal band). Anyone have pics?
One concern I have is oil pressure - which I'm not monitoring. Placing an oil cooler in parallel could lower pressure in the engine. I used an IR temp meter to look at inlet and outlet temps on each cooler; you may be right about a series setup ending up with lower oil temps. Need to do some more testing on it. My current thought is that the oil restriction in the factory line is causing it to be even more 'unbalanced' that it would otherwise be (like a 1k resistor and a 5 ohm resistor!)
-Joe