Feel free to experiment with as much 630nm wavelength as you want, but be sure to experiment with equal amounts of 660nm so that you can actually develop an accurate idea of what they do.
One reason I believe the 660nm wavelength to be such a good choice over any others is because it is smack dab in the middle between 630nm and 690nm.(Red and Deep Red) I believe 660nm has the capability to achieve the same results as combining 630nm and 690nm. In essence, it's the best of both worlds. As you can see from the chart below, the 630nm wavelength is actually closer to orange, not true red. Chlorophyll A peaks around 690nm while chlorophyll B peaks around 630nm. 660nm is conveniently right in the middle allowing a higher light absorption rate without having to use 2 different wavelengths.