I foot braked a Duster running 6.90-7.0 for years
What I found was --looser converter made car faster but....
I could cut way better lights with tighter converter
Stalling it hard as possible also enabled better lights
Once I quit caring about ET and tuned car for best reaction times and best lights it started winning!
Two steps and Transbrakes in footbrake is just like mixing chocolate and [censored]--it is silly--either footbrake the car or put a box in it!
You are fighting city hall
Drum front brakes on footbrake car are a MUST--they are self energizing--they HOLD the car 10 times better than disc--most winning footbrake cars have drums--there are ways are lighten them--been around for decades
Toss the brake or get a box
Brakes are the secret to Foot Braking
Loose super fast converters sink the whole set up
Leave RPM has to be consistent to cut good lights and win races--Period.
I am always amazed that folks are never seeking ways to WIN more races--
rather they fiddle with the mechanical aspects of the game
Those have to be understood for sure so your basic questions are super valid but if you want to win races study the guys and ask the guys that win lots of races --same ole guys win all the darn time and many can't even adjust a shifter--they just have learned How to Win!
Get the car where it will hook in a plowed field and is not so sensitive to track conditions--keep converter on tight side --work with all the things you have available like front tire pressure, shocks, big mirrors, staging technique--never forget the psych game--use it like you have a truckload of it to get rid of fast--Polite drivers do not win--
Then go win a race--amazing thing is after you get one they start to come easier and easier--pretty soon you are the guy they don't want to get beside--then they start beating themselves and you are da Man!

Converter choice should be about tuning car for best lights in a footbrake car--nothing else. ET should be just a result not the goal.

Nothing helps like trying several and just see what happens--you will find a favorite and win like crazy until it blows up--then you will have to buy several more to get another one like it--they are like cakes --same recipe from same baker--top looks different on every one!