A smaller NA reduces dispersion by limiting the number of modes. Fiber bandwidth is given in MHz-km. If you double the distance, you half the frequency. With singlemode fibers, the bandwidth for a 100-meter run is about 888 GHz. The bandwidth of a singlemode fiber is essentially infinite in that it surpasses the ability of today's electronics to exploit its capabilities.
Attenuation is loss of power.
During transit, light pulses lose some of their energy. Attenuation varies with the wavelength of light. The 1300-nm window offers lower loss, but at a modest increase in cost for LEDs.