I'd only buy the same version I knew worked for me online.. Shoe companies have a habit of messing around with shoes between versions, making it as likely that they'll work as not. Problem is if they don't, you won't know until it's too late to return them.
My local running shop does a 30 day returns policy if they recommend them to you following a bit of a run on the treadmill, worth the extra for me at least.
From what I remember of the course from a few years ago you should be OK with road shoes if you're happier in them, provided there's no substantial rain before the off. It's all well trodden paths, nothing loose or rocky
There's a mile or so of cattle trods which might get muddy, but then you just have to pick the best line through
Instead of looking at this as fitness training, think of it as efficiency training. While you may feel you are running easy @ 150bpm, imagine running at a similar pace with a hr @130 bpm. Then think how much faster you could run @ 150bpm if you had this efficiency.....