With only 5 acres of ground you intend to plow, the 40 hp tractor is plenty big enough, even with HST. It may not pull as hard as a geared machine, but with a 2 bottom plow it surely should do the job. It won't take very long to work 5 acres of ground, especially if it's been worked up before.
The deal with getting the cost of Ags and rims discounted from the price is great. Keep the turfs as you may find chains on turfs the best way to go with snow removal chores in winter, especially if you get ice. If you ever want to mow lawn with the thing, you will also want the turfs on there, although it seems a little large for that job unless you have a huge lawn area.
Keep in mind these comments are from a guy who lives on wooded ground. I can't use a lawn mower with more than a 44" deck.
300 hours on the DX29, 850 on the JD 240 and too many to count on the Cadet