fan kicks on soley based on ECT at 230, but there are many other variables and/or combination of variables that turn it on for other reasons.
You guys are funny with your temps. Try towing a 42' toyhauler with with an off road car in the back. Can't even tow level in the 220s. there is no "break point" at the numbers you list. They just fall into the extreme duty category- Talk to your ford dealer, even running constant 230-240 all the recommend action would be to increase your oil change interval. Truck starts to "prevent" heat issues from occuring by reducing power when you reach 250s, limp mode kicks in high 260s. Let her cool down, and she is ready to roll. Diesel equipment in Iraq runs 24/7 in the heat, constant 280 range, yes its different engines and all, but seals ect are all the same. Go to the track some time and see what the race engines run. mid 300s EOTs..... The level attention this issue gets with no real facts starts to get annoying after awhile, people seem to develop OCD on EOT and blame the 6.0 issues on it. 6.0 issues caused by faulty EGR components and overpowered tunes for heads, not to many directly related to high EOTs. But I digress...