Physically they are exactly the same. The double binning system is meant to increase your chances of getting what you want for your current requirements, since some people drive at low level and some at high. It's a bummer to get an LED that looks white at it's binned level, but see it turn green when you back the power off, or get blue when you light it up.
Somewhere in the complete bin code there is a mark that notes which of the two current levels that led was binned at. I honestly don't remember what it is but I think photonfanatic has a note about it in his sales thread. It doesn't neccesarily mean one is brighter than the other. It's sort of like the overdriven Lux I vs. underdriven Lux III debate. If you're only driving your K2 at say 350mA, you can buy one binned at the lower level and be sure the tint and brightness will be what you expect at that current level. If you drive it at an amp, it might look a bit different. Likewise, underdriving a K2 binned at higher current may result in some color tint shift. The same rules apply for vF.
