G'day CJN,
I've tried 3 different tweeters with a few different networks.
The K-77 is the one I like the least.
The K-77-M sounds better, but it was just to in my face when I was using the AL-3 or the ALK universal networks. It was a good match with the ES5800 although I still took a few dB's out of them.
The CT-125 seemed to be a good match for the ALK universals and also the ES4000, I found it to quite with the ES5800.
As far as my ears goes the CT-125 is the least sensitive followed by the K-77, and the most sensitive is the K-77-M.
I've never heard the K-55-V, I have only ever had the M's is mine and they sound OK. I did coat the K-400 with some sound defusion material.
Good luck in your choice.