4th is "near" 1:1 I'd have to look it up again but .947:1 comes to mind, close enough where it does not matter much. and to clear up confusion, typically numerically higher gears are a lower total. remember the : can also be documented as number of teeth. eg. 13/21 or 1:1.62 aka .619:1 they are all the same ratio but are all greater then 1:1 just how it's documented. treat the : as a division sign (putting the 2nd number on top) and it might make more sense to you. since when you divide1 by a number <1 you get an output >1..

however when you factor in the final drive ratio. (I'll use your vette example) 3.42:1 is where the overdrive ceases to be. since even at (6000 RPM / .570:1 (6th) = 10526RPM) then through the final drive which is 3.42:1 (10526rpm / 3.42= 3078 RPM. 3078/6000 1.949:1 engine to wheel ratio in 6th on a Vette, still numerically higher then 1:1 or a lower gear ratio then 1:1.

so really it's irrelevant what the transmission ratio is since the dyno has no idea, it does know wheel speed and it knows RPM (if your using a pickup) I don't know where the 1:1 dyno statement comes from? Most Tuners just try and find the gear that gives them the highest peak numbers on their given dyno. (since most dyno customers just want bragging rights anyway)

That's why I put little to no value in dyno numbers in compairing cars to one nother. as a tuning tool, sure! but proper power delivery is way more complicated then XXX max wheel horsepower. Using the Spec V vs. the Honda Civic Si for example. If you followed the dyno graphs the SI should distroy the Spec-V it's got 11% more peak power Also 6 speed, and LSD and is a bit lighter. but it Never does... Nissan put way more time into getting the Ratios correct to use 100% of availble torque and keeping that car in the meat of the torque curve is what makes it so dangerous on track. regardless if it's suspension was taken of an 18th century ox cart.