Ideally your oil should run in the 200-220 degree range. It actually works best at those temperatures. 230 degrees is getting quite hot, and by 240 the oil is starting to break down. 250 is the point at which the engine is derated, but IMO that's too late. I always advise anyone who's had this happen to get the oil changed ASAP. Once you cross 240 each degree is more and more dangerous and the oil breakdown is not linear with temperature; its exponential. The big issue is that oil takes a while to cool down. Unlike coolant, which is water based and great at rejecting heat, oil is not great at rejecting heat.
ECT of 240 is getting pretty hot, but with system pressure in the 6.0 it would take 250+ to get it to boil over.