Re: Difference b/w a 5 speed and a 6?
The gearing ratios are more important than the number of gears, but generally, 6-speeds are designed to have closer ratios so you can stay closer to the redline when shifting, and thus continuously produce the most power when accelerating hard. It only really helps in cars with peaky power curves and high redlines, like the RX-8, S2000, etc - cars with flatter torque curves, like the Mustang GT, do fine with 5-speeds. Older American cars used to do fine with 3-speed automatics just because of the sheer amount of torque coming out of the engine.
6-speeds can also help with fuel economy when cruising in top gear - the C6 Corvette's 6th gear has a ratio of 0.50 to 1, allowing it to get very good highway gas mileage because it can keep its revs nice and low, despite having a huge V8. You could do this with a 5-speed as well, but putting a big gap in between gears causes a sudden loss of acceleration when you have to shift into that fuel-economy gear. A 6-speed lets you get a more gradual transition that lets you accelerate effectively all the way up to crusing speed.