I put in the yellow spring + a spacer last night and it sounded like poo this morning on the way to work. I can't describe the noise, it was a hybrid pssh + something else.
Really though, I've tried yellow, blue, blue + spacer and yellow + spacer and the performance difference is negligible. To me there is a slightly different sound though.
Blue or Yellow, no spacers is probably a safe bet.
I have a black one a can let go for 130 dollars!
How long did it take to get to you? And I would like to hear your thoughts as well on the quality, noticeable improvements etc.. It would all be greatly appreciated! Gosh I just can't wait any longer.