BCM has their mid-length upper for $439... Add their BCG and extended charging handle for $70, and you're golden. Better barrel, better BCG, better charging handle, minimal difference in cost.
Either way, an M16 carrier weighs a little more, which can help slow the cycle rate and give the magazine more time to feed, and it also carries more momentum, which is helpful in feeding from gritty/dirty mags. It's marginal, and nothing I would care much about. The charging handle, on the other hand... once you use a quality extended one, it's hard to go back. If you're a guy that sits at a bench and shoots, the factory charging handle will be fine. If you do a lot of malfunction clearing drills and whatnot, then having one that is easier to grab and can be worked with one hand without risk of breaking the pin is great.