Questions about putting together a Ford 9"

[F23]

Hey guys,
I'm right at the start of modifying my 1969 Mercury Cougar as a pro-touring car, and I'm going to swap in gears and a posi into the 9in. I need some recommendations for what to do for each.

Background info:
Going to swap in G-Force T5 with either .63 or .59 overdrive
Mostly Unmodified engine makes ~315hp and ~390lbs
I will be making no engine modifications in the near future due to cost and time
It IS my daily driver
I have a VERY low budget



So, gear wise, I'm stuck between 3.89s and 4.11s. With the FMX and the 3.00 in the back, I'm turning 2500rpm at 65mph in 3rd(Top, 1.00) gear.
here are the various combinations and their rpm at 65mph with 27" tires

4.11s and .59=2040
4.11s and .63=2175
3.89s and .59=1928
3.89s and .63=2070

All of these are significantly lower (300-570rpm) than stock, so anything is an improvement. Of course, since I'm most probably overestimating the power figures, I want to get the most acceleration possible with the power I have. So I'm very tempted to go with the 4.11s and the .59 overdrive. The real problem I'm having is that the rpm drop from 4th to 5th. It's almost a 1400rpm drop! That sounds like a lot, but how much of a drop is it actually? Is it really hard to shift with that much of a drop? The drop from .63 is only marginally better, at around 1230rpm.
So the question is: is it worth it to have the acceleration benefits of 4.11s if the drop is that severe? How much of a difference would there be between the 3.89s and 4.11s? Opinions please

Onto the next, simpler question of the type of limited slip diff I want to out in. The 3 main types I've heard of are TracLoks, Truetracs, and Detroit Lockers. Keeping in mind that I am putting burnouts and quick, sharp handling infront of pure drag strip straight line speed and acceleration, but since I'm also using this car as my daily driver, in rain, sleet, rain, and everything in between, it has to be practical for everyday use, both in the parking lot and on the parkway. Keeping in mind my budget, what are your recommendations?

All RPM calculations were done on http://www.csgnetwork.com/multirpmcalc.html

Thank you,
F23