This sort of thing would come up all the time when Car and Driver would publish there top gear acceleration tests (30-50mph, 50-70mph IIRC). With most 6spd transmissions top gear at 30mph means the motors are way down on their torque curves. This resulted in may "slow" cars posting better numbers than the Corvette simply because those slow cars weren't nearly at idle during the test. It also resulted in most cars with automatics dominating the results because those cars would downshift while the manuals were required to stay in top gear. Also, I believe both the Viper and Corvette top out in 5th, not 6th gear. The Corvette and Viper boxes (really the same basic box) are double overdrive units. So their 5th gear is roughly equivalent to what many other cars were running as a 5th (back when 5spd manuals were the norm and 6spds were rare). The 6th gear was an extra tall ratio for high way cruising only and was never meant for any sort of performance at any speed. It was tall enough that the car would hit its drag limit before the motor reached peak torque. In short the ratio was only good for mileage (which it does deliver). Compare that to the gearbox in the MX-5 Miata. The 5 spd and 6 spd covered roughly the same range and top gear in each resulted in similar engine RPM for a given road speed. Basically those boxes just gave you a tighter set of ratios. For the MX-5 the taller 6th would have been welcome.
One final note, the 6spd auto in the Civic is geared rather like the Corvette. The top gear is very tall and only good for flat highway driving. That's no big deal since the car can quickly shift down to 5th for mild uphill sections. You get good highway mileage and decent passing power without a big downshift. Go Honda.