z3toz4 
2006 BMW Z4 Convertible 3.0si 2dr Convertible (3.0L 6cyl 6M)
Z4 3.0si
 I had my Z3 for twelve years, finally bought a Certified Z4.  Be very careful with Certified, even though BMW has fixed all the problems that have come up, mine has been in the shop for MAJOR suspension and engine problems.  It has been in the shop 20 of the 60 days I have owned it.  Not what I expected from a BMW Certified car.  Now that I think I am past the problems this car had, I really am enjoying driving it!  Much smoother, powerful ride than Z3.  