This is from another post I left in this same 300M forum:
Originally Posted by Candyman
I have the '04 Special. It's a sportier, firmer ride with the larger rims. A few more HP. HID headlights. The regular M's ride quieter, softer, smoother, more luxury than performance and handling. Specials also have the body kit and are a half inch lower than regular M's. Also, comes loaded with just about every feature offered for this vehicle line as standard.
The Specials are also a rarer find and breed then the regular 300M's as they were only produced for the '02, '03 and '04 model years.
Here are a couple good links for reading for more info:
As for fuel milage, I get about 23mpg with a 60/40 mix of highway/city driving, this using mid-grade octane. They say you need the Premium for the best performance, but I have never noticed anything different with using the mid-grade stuff. Saves a few pennies as well!
With all highway, I have reached 26mpg, all city around 19mpg. Although there are a few cases over on the 300Mclub forum or people getting 30+mpg with their Specials. A lot of it has to do with driving habits, climate, weight, etc.
For the performance and handling the Special offers, the gas milage is actually quite well IMO. Sure, I'd love to get 30mpg but with as heavy as this thing is as well as getting over 260HP (I added a cold air intake, performance boost of ~8HP) out of a 3.5L motor, sacrificing mpg is part of the equation.
So, if you're looking for a smoother, quieter luxury ride, stay with the regular 300M with the smaller rims. if you seek a sportier firmer and more exciting ride loaded to the gills with options, the Special is the way to go!
I LOVE my Special and would not trade down for a regular 300 if I had to. Not that there is anything wrong with them, they are just as sharp, but the Special is far more my style.
Good luck with your decision!