LEDs that aren't being battery powered, such as in a PC, can be brighter than you might expect. Personally, I think that two led strips with the length you mention will light fairly well, but everybody has their own opinions on what is the right amount, and the color may impact your perception more than the luminosity, as not everything you install into your chassis may play well with the red lighting. Obviously white or light colored LEDs will likely appear brighter, but 100 cm of LED lighting should be a good start. You can always add more if you want brighter illumination, and a mix of your color of choice plus white can work well for accenting along with appearing brighter.