Joining a band with some serious sound quality needs, I had to reconsider replacing my crashes.
K's are an absolute classics, no doubt that in a quiet, Pink Floyd-esque settings, this is a cymbal that will give the most complex and non-intrusive tone, sounding almost like a good gong, opening up with beautiful overtones.
For rock gigs, my old Z Customs were quite fine but top music in my mind requires top quality gear and for me, K's are just that.
Now there are many good cymbals and Zildjian is not the only cymbal company to provide top cymbals, and you can say that K's are really ancient but personally, hitting a decent K is a holyday to my ears ;)
I opted for 17 an 18 crashes and indeed in Thin version as this is where most of that beautiful shimmer lies. Medium thins would probably be more resilient to damage from strong hits and louder but Thins are nice and flexible, so taking some caution before bashing in exchange for beautiful tone is a good deal in my book.
Overall an amazing buy, highly reccomended.