I have both sleeves and I don't notice any difference in weight between the two. I find the light easier to use with the gaurded pack due to its slightly longer length. If you pocket your light most of the time then you might like the NG sleeve since its slimmer. Better yet just get both!
Another question - The regular production light using the Seoul - does it get hot and step down as quickly as the K2 led, or is the Production version better in that regard?