My LR4 has much stronger braking power (stock) than my V8 HSE LR3 (stock). Going to the V6 LR3 brakes, adding a bunch of overlanding kit is asking for issues IMO. If you do go that route buy really really good V6 rotors/pads/stainless lines etc. Everything. Would be cool to see 17"s though.
I'd rather shell out the extra $$ for LR4 compatible 18" rims rather than downsize on brakes... That being said, I'm swapping out my TuffAnts for Defender Steelies this weekend as I love the classic aesthetic of the white wheels.