Quick comparison between an unmodified D600 and full-spectrum A6000, using the same 18-35mm AF-D lens at f/5.6 and external 720nm filter. D600 shot at 28mm, A6000 shot at 18mm to give equivalent field of view.

Basically, when you combine a filter that cuts 95% of visible light with one that cuts 99% of infrared, you get a lot more visible light coming through in comparison. The result is reminiscent of a 590-650nm or so filter.