I bought my last truck (an F250) on a Wednesday and by Thursday was wishing I had spent the extra $1000 (closest I could get the dealer) for an F350 for no other reason than some weird mix of buyer's remorse and "I want the next step up-itis"....but that was buying new. If your current F250 setup works, why change it?
If I were buying new, I'd buy within all the ratings, just 'cause that's how I like to do it; but if you've put the miles and time in on your rig and nothing's blown up, started to sag, drip fluids, rub, etc., I can't see a basis to change.