I would suggest the cable version. if the cables are too short you can increase yourself.
The thing is, the higher the watts, the more the LEDs can stand out from reflections/sunlight etc.. But the normal Wii remote bar only has so few watts. With the LK-software, you just have to make sure that it doesn't get confused, as the wii remote can only evaluate 4 IR light sources. Higher watts makes it more easy for the software because you can decrease the sensitivity. But the IRs can also produce reflections and they are brighter with higher watt leds aswell. Selfmade IR-Emissions, natural IR emissions, IR emission from other devices.
The official website only mention the 3w as a suggestion since the author made this as a hobbyproject and can't evaluate every situation if it is realy worth to use these bright IR-LEDs. Also the author don't use the original nm wavelength from the official wii remote bar aswell. I would suggest stick to official wavelength since nintendo designed the wii remote in junction to the ir-bars.
The author shouldn't be such a lazy one not to adjust the documentation -.-.