Re: Just how firm is the 997 GT3?
I cannot compare it to the M3 CSL but I can speak of the 996GT3 vs 997GT3. I live in Mississippi and I'll bet our roads are at least as bad as UK roads. The 996GT3 was miserable on our roads particularly dealing with sharp bumps like expansion joints, it tramlined severely and was very "darty" on the grooves caused by semi trucks. I hated driving it. I dreaded hitting the bridges on the highway because there is a slight rise when you enter and exit and it would literally rattle your jaw. I like having a stiff ride but that was ridiculous for daily driving.
The 997GT3 is a revelation. It does not send shock waves into the car on sharp bumps and is very livable. There is significant road and engine noise so making mobile phone calls is a challenge. I love driving it on a daily basis and is "comfortable". For most it would probably be too jarring but I found the 997Turbo too soft. Funny thing is that it handles better, has more grip, is faster, and more comfortable than the 996GT3. It is the perfect Porsche for me and cannot imagine how Porsche is going to top this, no wonder CAR magazine called this the "greatest 911 of all time".
I have never driven the M3 CSL but my hunch is that the 997GT3 is tuned a little stiffer and the 996 GT3 is a lot stiffer.