Unless the boiler is smart enough to raise the supply temperature by zone, you probably want 180-degrees going into the indirect to get reasonable recovery rate. Most radiators are desgined for that temperature, too. To keep the thing from short cycling (it works best if it runs for awhile), you might want to try something like 200-160. See what the pros have to say. The new, smarter controls will adjust the boiler temperature for the needs, and might only run say 140-degrees on a mild day to keep them on longer rather than cycyling on and off at a higher temp. You don't have that option. They combine this with a variable burner, but I don't think they've been able to do that for an oil burner, only gas.