my 2011 250 has 1 less overload spring compared to the 350
Not sure what you mean but there is only one overload spring on each side. You either have one or you don't. They are separated from the main spring pack sitting on top.
Ok it has one less spring in the main pack
I think your off in that payload number (might be whats in the brochure)
look at the yellow sticker inside the drivers door it will show the actual payload for your truck with the options you have.
Still getting it weighed as mentioned is the best way