Affordable 5 or 6 speed transmissions?

The 4 speed OD is the cheapest way to go, but has a big RPM drop between the gears. I have 3.91's with a Tremec 5 speed. The gear spacing is fine and the 0.64 overdrive let's you cruise at 80 all day. The Passon 855 is the easiest to install, just a direct bolt in. The six speed is heavier and should have more parasitic loss. Anybody on here with a T56 in an A body?