What Delta T should I use on boiler loop?

I am getting ready to fire up my system for the season ( I know, I'm late) . I have a Taco 0012 Δ T Circulator on my boiler loop. The boiler will feed a 500 gallon propane tank. The Taco Δ T can be set to a range of 5-50 degree ΔT. I have no idea how long a burn it will take to charge the 500 gallon storage tank, but I'm guessing about an hour or so. I have a Seton 130 and my run length to the storage is only 40 feet thru 1 1/4" black pipe that is well insulated. I should be able to push a lot of water, the runs have only a few 90's both ways.

Assuming a storage tank return temp of 150F, I would think a larger ΔT of 30 degrees or so would be good to start with, but as storage temps rise, you would want a smaller ΔT to keep from short cycling. (I have a baffle pipe welded into the tank to provide excellent startification, so I should be able to keep the return temps as low as possible for most of the cycle). I would like to get 190-195F water in the tank, and am thinking I would want to my draft to close at about 185-190F.

However, I don't want to have to be adjusting the ΔT on the Taco in the middle of the burn to get the desired flow, so should I just leave it set for a 20 degree ΔT ? The circulator will run continously, but slows down or speeds up automatically to maintain the set ΔT. So, if I set it for a 20 degree differential, as storage return temps get to about 170F, the boiler should shut down and the circulator will adjust flow to maintain 190F water back to storage, until the boiler cools too much to maintain that temp, but it should do this for quite a while I would think.

thoughts?

thx, Pat