I wouldn't pay more than at least $10,000 off MSRP for any of the big three HD trucks. You may not get that from the dealer down the street but the volume dealers get a lot of kickbacks from the manufacturers so invoice or xplan or whatever is pretty meaningless, imo. I'm not trying to rain on your parade at all and if you're happy with the deal go for it. You do have a nice big advantage on sales tax that most of us can't avoid so that helps make up for the less than stellar price.
One other consideration is the 2017 MY Super Duty is going to be all new, so you could wait and see if you like it better and if not, you could probably score a killer deal on a holdover 2016. Just something to consider.