Guys, quit comparing...ummm...wrenches.
To OP, all things being equal, you need to drop the ball/head by 3". But since all things are not equal (F250 will not squat as much as F150 under load), you may actually need to drop it more than 3" to end up with a level trailer, assuming you were level before.
Standard hole-spacing on any WDH shank is 1¼". So 2 holes down is 2.5"; 3 holes down is 3.75". If you were a bit tongue-high before, go down 3 holes. If a bit tongue-low before, try 2 holes down.
Either way, that's a starting point. You need to do a complete re-check on the F250, measuring the front wheel well height before and after attaching trailer and engaging WDH. You want that height to be back to stock for best handling.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller