Don't buy a cheap tire for a quality high-power car.
The KDW is a good tire, but suffers from noise and wear issues. Having been in and around tires for my entire working life, I assure you any money put into a good set of 4 tires on your Z will open your eyes like nothing else.
Also, you should consider your goals and wants to determine your tire choice. Weight in on things in the list here:
zerothread/17514
My feelings on the origional RE040's on my Z were that they were over-priced for the grip and wear they gave me. I ahve since had BFG G-Force KD's (yeah, the super sticky dry ones), as well as being a test dummy for a set of Continental Contisport Contact 3's. BOth tires are good..but have different goals in mind.
I ended up running a set of ADVAN Sport's, which are kickass. Just as grippy as my KD's, low noise, good wet weather, and with 10k on them, good wear.
Anyways, what's your goal for the car, how you use it? budget? let me know and I can help steer you in the right direction..
-Chet
you can also find my (albeit old) tire reviews and facts in the wheels/tires forums.