The 4 strokes make more torque, but are limited to about half the practical RPM range that an equivalent 2 stroke motor makes. It's not really the fact that it is a 4 stroke that does this, but the way the head and cam are designed to create that power. Since most stationary style forced cooling engines are meant to live long lives running at happy stable RPMs in all conditions, it makes the most sense to have a lot of low rpm power.
The 2 stroke kits... not so much. In fact, properly tuned 2 strokes can produce a stupid amount of torque at low rpm's too. Just like the 4 strokes, it just depends on how they decided to setup the way they are tuned to make that power.
If a 49cc 4 stroke makes 1.5hp and has a max RPM of 3600, and the 49cc 2 stroke also makes 1.5hp, but has a max RPM of 7200 (For sake of argument), and it just so happens the 2 stroke makes half the torque of the 4 stroke... The 2 stroke can have double the gear reduction, both bikes will achieve the same speed at their respective maximum RPM, and the torque delivered through the rear wheel to the ground will be numerically the same you just then have to ask yourself if you prefer the smell of 2 stroke oil or not.
The only real advantage 4 strokes have over 2 strokes at the end of the day is efficiency, and sounding like a lawnmower instead of a weedwacker.