Order an 08 model. you will get more HP, and you can build it exactly the way you want.
As far as the F55. Awsome. Since 07 the F55 gets the larger sway bars and bigger brakes along with the EOC. The F55 always got the upgraded tires just like the Z51. They are the f1 supercar EMT tires.
I track my car every chance I can and the F55 holds up great, that s coming not just from me but from my instructors coming off of Z06s. Very little performance diff between z51 and f55 now adays, but the ride in the f55 is sweet. The Z51 is not bad in the street unless you have a lot of bad roads.
The F55 does take a little getting use to on the track.
The F55 works with the active handling system, so in the street it will help in some situations ( it can change the handling on 1 shock to compensate for conditions the active handling system is helping with...overbraking in a curve and so on, so it is an added saftey feature if you think about it)
If I order an 08 it will be set up the same as my 06 for the most part. If I wanted more performance I wouldn't get a Z51, I would get a Z06, but I like my convertable so no Z06 for me this year.
No matter what you get the C6 is an all around great car.