I'm inclined towards B because I like a longer sighting distance. The foregrip will help with forward weight/balance. The stock does nothing for me personally. I do really, really like the Magpul PRS though. The extra bit of rear weight will off set the front weight and the adjustability will put you in that 'comfort zone' and let you stay there longer with less muscle strain.
Both look good. A is probably very similar to what you already have. B will move you in another direction and give you some versatility––- all depending on your intended uses.
For a BUIS, the LaRue iron is about as clean, streamlined and rock solid as they could ever be. Once it's on the rifle and aligned, you'll never have to touch it again. Beautiful, brutally efficient, unobtrusive simplicity.