In reply to Tom Last:
I used to own the Guides but worked in a gear shop so tried the Rebel Ultra on as well on different occasions. I found the Phantom Guide to be a wider boot and had more volume in it, which suited my wide feet quite well. I'd say the Rebel Ultra runs pretty much the same in sizing as the Guide but might be worthwhile bearing in mind what I found with them being slightly wider in regards to sizing. Try them on if at all possible before committing to that amount of money.
My Guides gave up after a season of use so they got sent back and were replaced with the new Phantom Tech which I think is a great boot for technical climbing but still keeps its warmth very well, a bridge between the Phantom Guide and the old Phantom Ultra.
Would recommend the Phantom Tech as another option worth looking at, very good all round winter boot, flexible enough to give comfortable walk in but still perfectly capable when you stick a crampon on them (have used Darts and Rambo 4's with mine and both fit great).