Grumpy_Mike:
do those LEDs really need such big heatsinks to function properly.
I have no idea because you haven't said what you are going to run them at and you have not given a link to the data sheet. I suspect you don't have the data sheet yourself, so we are both guessing.
Yes, you are right, but I don't think those LEDs differ very much... As far as I saw on ebay, all of them use 3.4-3.7V and 300-350mA.