Good looking rows there MM. I've tried different variants of the "stacking" (gosh I wish someone would invent a machine that you just throw the wood splits in and the thing walks down a path while making a stack) At any rate, the fastest way (and not saying you're looking for the fastest way) I've found is to split at the stack. (Actually, I do everything right at the splitter including bucking the logs) I figured I had to bend over anyway with the bucket full of splits for the bottom rows (in your case the wheel barrow). I just let a pile of splits grow about 2' tall and just sort of place or kick them from the pile right on the rails. Less wood handling which I like.
Everyone does things differently to feed their inner soul.