I did a test with "Dan Gurney's All-American" synthetic oil, in the mid-1970s, at Riverside raceway, a 95-degree day, and an S-W electric oil temperature gauge.
Ran one half-hour practice session (full GP course with the mile-and-a-tenth straightaway) early in the morning, noted the oil temperature on the last 'hot' lap. Drained out the Castrol (GTX 20-50 IIRC), replaced the filter with new-same, and refilled with the Gurney synthetic.
Ran the next session, just before noon, day had heated up a few degrees, noted the oil temperature on the last hot lap was 10 degrees cooler than at the end of the first session. Lap times were improved, but not more than what I'd learned to expect as a result of practice and tire-pressure trimming - which may have been in the wrong direction and cancelled or masked any improvement due to the oil, but I didn't think so.
That's it. Close as I can get to "science".
I have no idea if the synthetic of those days would be "full" or blend, or what it might have been in any respect other than it had Gurney's name on it and cost nearly ten dollars a quart.