Plenty of early '80s microcomputer systems with 16-colour graphics offered digital RGBI output: four TTL (or at least digital on/off) signals for red, green, blue and intensity. These included many models from NEC, Hitachi, Fujitsu and Sharp, IBM PC CGA, some later MSX machines, and the Commodore 128. All of these were "NTSC compatible" in having 240 line progressive output (generally with 200 lines displayed) and using a horizontal sync frequency of around 15.7 kHz.
Were there any systems using RGBI that used a significantly different sync frequency in order to display more lines? I'm looking specifically for RGBI output at these higher frequencies; IBM's EGA, for example, does not fit this because it uses RrGgBb in its higher resolution modes.