3S gearing, I'm shocked!

[foreveralone]

Hey all,
While I have enjoyed an '88 Conquest TSi 5-speed, a '95 Probe GT 5-speed, and an '85 300ZX 5-speed, I'm mostly a Camaro / Firebird guy, except for a few Mustangs.
I did a carbureted 5.7L '78 Camaro that managed 25.1 MPG at 65 MPH with the ignition advance being way late. I used a 700R-4 automatic, and was geared for 1800 RPM. A year later, I drove a second-gen Eclipse 4-cylinder, which, to my extreme amazement, would also cruise along at 65 MPG doing just 1800 RPM! Great!
Just now, unable to sleep, I looked up all the gearing options ever used on any / every version of these cars. Very sad. The best possibility is the 6-speed, which is 1940 at 65! Can any of these cars even see 25 MPG? And my automatic, ( which is geared identically to '90s Cummins-powered Rams ), is 2300 at 65! Even then, it doesn't have enough first gear, even with the 3.958:1 final. We get a 10.1:1 first, when I know from experience that an 11.4:1 is great for a similar-weight, same-tire-diameter '88 IROC-Z 5.7L with a shorter-runner intake manifold.
I can see I'll need to do a 6-speed swap to like this car. Yet having done the whole Fiero thing, I'm thinking of the F40-MT2, ( not Ferrari ) which would require custom axles, flipping the engine around 180*( or outright swapping a GM V6, in my case ) and would give a cruise RPM of 1870. Plus the trans itself can be had new for under $1,000 delivered, and has proven strong enough for 500 HP V8 swaps. Ratios are 3.7692 / 2.0400 / 1.3208 / 0.9538 / 0.7547 / 0.6208 with a 3.5455:1 final.