I can't speak to Cusco, because I have never used them. But I have driven/set up/ installed KW on many cars. They are well respected in the industry by impartial folks who know what they are talking about. The spring rates are likely softer than the JDM options, but that does not mean they aren't as "aggressive" or "fast". They have some of the best valving in the industry. My time attack miata ran KWs for a while with softer spring rates than spec miatas and was significantly faster. To me, they are one of the best options for street/track applications. Go search for them on
www.motoiq.com for more technical info.
The other option to consider is AST. I confirmed with them earlier this week that my set is currently being built in Holland and will be here in a couple weeks. Their new 4150 series incorporates brand new updates to valving and technology. The FR-S/BR-S system will be the first platform with these updates. looking forward to getting them.