Does the kickdown cable available for the 700r4 allow you to have full throttle acceleration in overdrive, or does it just allow a maximun of two third throttle?

also how many more mph are you going to see top end with 2/3 throttle in od versus full throttle in 3rd

 

The kick down cable won't give you full throttle in OD. The 2/3's throttle limiter inside the tranny.
The top end difference depends on your gear ratio and engine power.

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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

 

the car has a 3.73 rear, and is making around 240-250 horsepower. right now it hits redline at about 100mph(then end of a 1/4 mile run for me). what would the top end difference be with thoose numbers?