Ok,
I'm looking at either the 18x10/18x9 setup from Mustang Tuning OR the setup from Wheel Replicas. The offset is the same on the regular 18x9's for both companies at +24mm. But, the rears are different for each company? Mustang Tuning's is +45mm for the 2005+ deep dishes and Wheel Replica's are at +22mm.
Reasoning? Does that mean that the ones from Wheel Replica's have a deeper lip and mount farther in? I like the staggered look shown in their customers photos at the main page. They put their regular 18x9's up front and the deep dish 18x10's in the back.

 

18x10 with a 45mm offset is the proper setup. That is what I have on the back of my car.

use this tire calculator

http://www.bigcustomwheels.com/info_specs.jsp

just set it up so you have the same size tire (ie:285/40) on an 18x10 rim and set one to +24 and the other to +45. You will see there is almost a 1" difference. The +24 will have a wider lip but will also stick out past the wheelwell by the looks of things. You can also put the stock settings in for the first tire and then compare it to the second tire. At the bottom it will give you a basic description of things to look out for.

The +45 will stick out 1" further than stock. The +24 will stick out 1.8" further than stock.

 

We recommend a 43mm offset on an 18X9 wheel and a 50mm offset on an 18X10 on the new S197 mustangs this also holds true for 19 and 20-inch wheels. We achieved these specs through our SEMA Technology Transfer with Ford.

 

Hey thanks everybody for the info. That tire calculator site is GREAT!

 

Thanks for the website John! That was very informative.

 

Aren't Mustang Tuning's wheels made by Wheel Replicas?
I know for a fact the FR500 replicas they carry are made by them. Not sure about the deep dish Bullitts.