Take them all with you as course conditions on the day will help make the choice. Personally I don't like to go too long, on drying or hard trails with fellcross as the stud spacing can make it uncomfortable and stud length ruins efficiency over hard packed trail.
The fellraiser and speedcross are much more forgiving across varying terrain in my opinion but lack forefoot protection. If the course requires banzai descent down a rocky trail prepare for pain!
On a user friendly trails, hard pack or dry then the mantra will come into play. Ive actually ran these in fairly muddy conditions as well and they were.....ok but I wouldn't like to be barrelling down a technical trail with them and the traction simple is not there.
The warmth/burning would usually indicate youre well on youre way to blistering if its a friction issue....which is never fun. Not everyone can get away with them but you could try a apir of twin skin socks. Personally i often find Hilly twin skin a reliable brand. If you do try some i would recommend using the smallesy size you can get away with, this simply helps reduce the chance of the layers folding/creasing up and causing pressure areas.
Personally i wouldnt even entertain the Newtons, there priced.....well its just madness,lol.
Minimalist is not for everyone and can cause just as many injuries as when wearing 'normal' running shoes. Ofcourse it has its uses, i sometimes use minimalist a part of active recovery and on occasion with use barefoot on the beach(in the warm north sea,lol).
Are you a neutral forefoot striker already?
Do you NEED to change?
If you want to try 'natural' or 'barefoot' dont buy any shoes, just get yourself down to the beach or find a field where you can have a bit of a jog about with no shoes. its really not all its cracked up to be and if you running now pretty much trouble free that is whats most important.
@Canary, the guy at the running shop either has no idea on the technology and devleopment in each Nike shoe or is an idiot.......... or both,lol.
You ideally need a better setup before thining about dropping 15-20 second per mile over marathon distance of such a low weekly mileage. More than likly 9.45 is going to be your race pace. The Hyde Park will be a good indicator however may be a very bad idea for someone who is operating of such low mileage, in terms of timescaling i mean. I think it may be more beneficial to do a 'test' over a shorter...maybe 10k and use a calc(mcmillan) to give you an idea on where your fitness is.