i'm not too familier with either of those 2 models but i know like stepping on any rock your going to feel the jagged edges of the rock and so on. THe idea is to build up stronger feet and this becomes less of an issue. I've stomped some rocks while running in them and it hurts etc..
as for sizing i'm like a 10 to 10.5 in any US shoe but in vibrams a 41 fits me prety good and that one says its for US 9 to 9.5. But I also like a little room at the top of the shoe myself I guess if i wanted my shoes to be tight and my toe to be mashed up at the top of the shoe ic ould stuff my foot in a 9.5 or a 9 I would not be happy however.
if you order from online then be sure youc an exchange etc... I'd personally like to try on the next size down myself but I have tried on a 42 and that was far to big. I do sometimes wonder if a 40 would fit be metter then a 41 but if it where I doubt i'd be able to fit a sock on my foot and the shoe.
if you want to be able to really feel things and grip them i'd get an even thinner sole I think they publis the stack height or thickness of the soles you can use that as a reference.