My opinion is the Flex is a great machine, but not the one to have if you're only going to have ONE machine. The PC is more than capable of doing most corrections in most situations, is great for light polishing, upkeep, and applying products. Heavier correction might take a couple of additional passes, but for the mostpart the PC is gonna get the job done.
We sell both and if you were shopping for your first machine I'd steer you towards the PC over the Flex.
Also consider that if you your cars in relatively good shape (which I'd assume a newer Z would be) then the added ability of the Flex might just be a waste as you'll never need that much polishing ability.
Heres a nice comparison using our new severe swirl remover and Flex vs. PC I helped a good customer of ours do on his mother in laws tahoe. Made the perfect vehicle for testing purposes.
http://www.youtube.com/v/ir8mA4vbgoI