Unfortunately, not all gearboxes are created equal, so there's hardly a time when a manufacturer creates both a 4-speed and a 5-speed box wherein the first four gears are the same.
It's simply because the five gear car doesn't have any more power than the four gear car, so a higher overdrive gear isn't required, as 4th gear is already designed as an "optimum" overdrive for that car.
Thus, in common practice, both the four gear and the five gear box have similar overdrive ratios (4th = 5th), with the 5 gear box having closer gears.
On some performance cars, 5th gear isn't even close to the overdrive ratio on the automatic 4-speed version of the car. On most cars, 4th gear or 5th gear is so tall that you'll never hit redline... on my car, top speed is limited by redline in 5th...
The 4-gear Lancer SL is a smaller car, so it can be quicker off the line than the GSR. You need to compare like-to-like cars here.
There's little advantage, nowadays, to building a four-speed box over a five-speed one... just a difference of one gear inside the box. The advantages for building a five-speed box lie in flexibility and fuel economy.
For six speed boxes? That's when you start getting higher and higher overdrives... as giving extra-short ratios at low speeds on a 6-speed MT means the driver has to row like crazy at traffic speeds. That's why 7-speed and 8-speed boxes are mostly automatic. Those extra gears make for more smoothness, but they'd make it a pain to shift it yourself...
