Well, I gave up on trying to find big, cheap, used urn.
The restaurant supply store had a 101 cup by RegalWare for $109 + tax.
I ran a test with the basket in to see what temps would result.
It heated 4 gallons from 60F to 212F in 76 minutes.
Steady 2F per minute up until 180F.
Then 4 min to 200F
5 more min to 210F then 5 more min to 212F and 5 min at 212F before it switched over to the warming element.
The temp dropped to 200F in the first 15 min,
then lost 2F per 15 min after that.
It definitely heats faster than my electric range.
But the basket makes to much racket to use when I'm sleeping.
I'm going to run another test without the basket.