I am a little late to this discussion. however, I have owned 18 Ford F250/F350 pickups, 1996 - 2000 models. all diesels. I have also owned a 2010 F250 with the V10. I had a partime business buying and selling these used Powerstrokes, and used them in my business.
GET THE DIESEL!!!!!
The V10 will eat you alive on gas cost. Average MPG will be 9mpg, at the best. Mine cost me $130/week to fill up, and I was only putting a few miles/week on it pulling my trailer. This was last spring, before gas went up again.
The mileage means nothing on the diesel truck, if it has had routine maint. and care. All my Powerstrokes had between 125,000 and 135,000 miles when I bought them. I sold many of them to friends who still have them. Miles on several are now around 500,000, and the trucks are still running strong.
Over here, I could easily sell the diesel you are looking at for close to $5000.00 in no time, on Craigslist.