Standard Z = 2003 - 2006 ......276bhp
Facelift version = MY06 onwards (this refers to a range of small improvements on these models, eg., improved quality interior, speed sensitive power steering and LED rear taillight cluster - plus other things) .......296bhp
Bonnet Bulge = MY07 onwards (taller engine 'with 80% new components', apparently) .......313bhp
Edited to add bhp's
DE is still the quickest down the quarter of a mile though
I've read that before, still don't believe it though.