Your experience with an oil/coolant heat exchanger is right on the money.
On my vehicles without one, the oil temp lags the coolant temp significantly and does not get to "normal operating temp" even after long continous runs. This has been my experience with both Modular V8's that had oil temp sensors. A 4.6 L V8 3V with a 6 qt sump and and a 5.4 3V with a 7 qt sump. Oil temps in below zero weather would stay a solid 20+ degrees cooler than regular weather even after long runs over an hour...
On vehicles with an effective exchange, they stabilize as normal.