Skymaster ownership costs: 2015 edition

[YankeeClipper]

Hi all. I'm prospecting for a Skymaster and have put together a spreadsheet of operating (really, owning) costs (snippet in attachment). Was wondering if anyone would care to comment on the reality of these numbers for 2015/2016. The "payments" are based on a roughly 90k aircraft (details were determined by loan calc, so assume the payment is correct). I also raised the tie-down to $150, but forgot to note that at the top left (where it still says $125). I've also assumed the 185-190Kt speeds that I've seen others recall as taking 24ish gph for the turbo. Perhaps then my annual and O/H is too conservative a budget?

Thanks.