I have the stock sprockets on my bike and am looking for a little more low end grunt.....
Years ago on my 1987 TW200 I switched to a 14/55 setup to take advantage of a specific local off-road area (small, tight trails, and short but very steep hills, with no rock at all - soft forest loam and/or clay). I didn't mind the loss of 10% of the top speed since the "play area" was only 3 miles from home. By switching to a 55 tooth rear sprocket, I got the engine speed right up to the torque curve literally at walking speeds! I could climb slowly up "steps" in the hillside, one step at a time at walking speed or less, and was the envy of many with faster bikes.
But I quickly learned I'd gone too far. The TW already has an extremely low 1st gear. I found I couldn't lower my rear tire pressure to further increase traction, since that effectively decreased the circumference of the rear tire and thus further reduced the final drive ratio, especially noticeable in 1st gear. Truth is, I basically lost the use of 1st gear in many circumstances and ended up climbing most hills in second gear. Frankly, some short very steep hills are best climbed with more speed due to the limited traction of loose soil or slick clay. By making such a major change, to 55 teeth on the rear sprocket, I drastically reduced the utility of 1st gear.
So if I needed more low end grunt on my stock 2001 TW, I'd certainly agree with the others above that 14/52 would be the first ratio I'd try. I suspect that would allow me to get pretty close to 14/55 just by letting air out of the rear tire. And if speed up the hill was more valuable than increased traction, leaving the air in the tire would retain the "higher/faster" final drive ratio, and create a little tire slippage when needed.
Only in special circumstances - like where all your time is spent rock-crawling - would it seem to make sense to take a TW with stock knobbies beyond 14/52. But hey, that's why they sell different sprockets!
- - - Happy Trails, Jim