Do I wait for the 5 speed?

We built this car back in 2007. Did a Hot Rod Power Tour. 451 B engine and a Passion 4 speed over drive.3.73 rear.
Car put down 20 MPG during and was fun to drive.
This is what we noticed.Anywhere we drove if you romped on it you would redline first to second, second to third and ran out of road I.E. already over the 100 mph mark,or a curve ahead,or traffic etc.
Now I had a Tremec 5 speed in a B body and it was ok but after using the Passion 4 speed OD I/we really prefer the Passion box. Not that there is anything wrong with a 5 or 6 speed if that is what you want. But do you really need those extra gears ?
P.S. We also did a Tremec 5 in a Duster using 3.55 rear and the car would lug (Because of the cam) at speeds below 65.
Just my thought on this subject. Price is much better too.

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OK , that is more in line with what I’m trying to find out. Thanks for answering. I still would like to get other thoughts and am kinda leaning towards the 18 spline Passon OD kit.