If the 7.5 FX allows you to ride comfortably, go for it. Find a club, and ride -- lots. Aim for 150 miles per week, with at least one or two century rides, as you get nearer to the event. Since you don't have race aspirations, just ride at your normal pace minus a mph or so and you'll do fine.

If the upright bothers your neck, even as upright as you can get it, then consider a 'sport' model recumbent.