Here are the ratios of my modified TSX 6 speed transmission which will be going in my Insight, next to the 6AT in the Ford Transit Connect I drive for work.
I like the ratios in my van pretty well; it's quick off the line (especially with torque converter) and even has some wheelspin problems when conditions are remotely slick. It has a good highway 6th gear as well: 2077RPM @ 65mph out of a Mazda 2.5L in a small van isn't half bad, and right now I'm able to get just under 30mpg @ 55mph with a pair of ladders on the roof, wet roads, normally inflated tires and temperatures outside around or below freezing. I think the top gear could be a little taller but if it were a full ratio taller it might not spend much time at all in that gear, what with the ladders I have on the roof.
I'd say with the spacing of the gears, a 7th gear to bring them all a little closer together and maybe push the top gear just a hair taller wouldn't be unwelcome. 5 speeds with the same spread would probably affect drivability. 9 or 10 gears? Yeah, probably too much.
