I have 2 83 490s and both are 4 speeds. I am converting 1 to a 5 speed, possibly the other one as well.
I don't race though, I've heard different things from other people but as far as the trails are concerned, the 4 speed just makes it hard to ride, all the gears are very tall. 1st gear does like 30 to 40, 2nd does like 50, 3rd does like 65 and 4th does like 75 to 80. I put a 56 tooth sprocket on the rear to tone it down and it really didn't tone it down all that much.
The power though is there, on roads you can putt around in basically any gear without knowing it, has tons of power from the bottom but on a trail you basically have 1 gear. After riding that bike one day I rode my friend's KTM 300 XC up the street. My first thought was, WTF? how many gears does this thing have? 1000? Have to shift so much to get up speed.
That's the thing that is a plus, if you want to drag race that 4 speed is much better than a 5 speed, especially if the 1st gear is low on the 5 speed. That bike takes off and you can run through the gears very quick, even if another bike may be faster if the first gew gears are too low you'll get the drop on them. Since I trail ride though I think a lower first gear would make it easier to ride.
1983 Maico 490 Beast