The Z35 is 105 shifters, FD and RD. The Z45 is Tiagra shifters, Sora FD and 105 RD. The cranksets are different also (perhaps to match the drivetrains?) but both use the Hollowtech II BB. The wheels are the same.
The MSRP's are $2199 and $1799 respectively. I certainly don't see where the Z35 is a $400 better bike, much less $200. I'd say (unless there's a big difference that I'm not seeing) go with the Z45, and if the Sora FD is just junk, you could upgrade it for much less than $200.
Last edited by LarryMelman; 07-17-09 at 05:08 PM.