If the cats are clogged to death 100% no question about it,

will this cause the car to not rev through driving gears less quickly than it normally would with a free-er flowing exhaust?

How drastic?

My guess is yes it wouldnt go through the gears fast and at a higher gear would be worse.

Cheers
ZIp

 

A clogged cat will cause all sorts of problems, but the most noticable is a major lack of power everywhere.