The 4L80E shares a very good portion of its components with the Turbo 400, most notable difference is the overdrive and electronic shifting.
THe 4L60E is the electronic version of the 700R4.
Correct me if I'm wrong, but imho the 4L60E would be plenty strong for a Z.
http://www.hotrod.com/techarticles/gm_4l80e_automatic_transmission_review/
Picture of the 4L80E, 4L60 / 700R4, and Turbo 400, article on the 4L80E in hot rod applications.