Can they be significantly lower than the Tanabe GF210?

 

http://www.tein.com/nissan.html

They do give you all the min and max specs on their web site.

-2.4 front -1.1 rear

If the rear reuses the oem upper spring seat and I kinda think it does. You can pull the oem upper spring seat out and cut it then clean it up with a dremel for a additional .8" rear drop bringing you to a -2.4"/-1.9" drop.