Actually the frames are almost the exact same. The wheel base is different but it was done in the rear suspension. There are not that many difference in the driveline of a C5 vs. a C6. The longer wheel base does make a difference in the way the car rides though, they do seem to ride better. Although I think it depends on what you are comparing, if you compare a 60,000 mile C5 to a new C6, then hands down the C6 is going to win. A new C5 ride really well also, the biggest issue is tire noise, if you put a set of PS2's on a C5 they tend to ride really well in stock form. If the car has been lowered you can forget about it. The stock shocks are too long in the cars to begin with, so when you lower them even an inch you end up riding on the bump stop which makes for a very hard ride.
I recently had a customer with a 89 that only had 1800 miles on it and I forgot how great those cars were when they were new. I am a big fan of the C4, I had forgotten how nice they were when they were not ragged out or modified.
On a side not a customer just came in here the other day with a 84 that had 200 miles on it. Yes not a typo it had 200 miles, he had just purchased it and it had 107 when it was delivered to him. He is going to drive it I believe, but wow, I can't think of the last time I saw an 84 that was clean and all of the interior fit properly.
Justin