Sorry for bumping this thread, but I just wanted to chime in on this. The reported refresh rate of 48.92Hz is due to the fact that the clock rates of these systems are left as NTSC. Performing a complete conversion with a swapped out crystal etc. would make a system like this run at the proper ~49.92Hz.
49.92 * 313 * 794,5 = 12.41Mhz (Standard PAL)
48.94 * 313 * 794,5 = 12.17Mhz (PAL game with NTSC clock)
Not too sure about the value of 794,5 for dots per line, but it’s probably close enough.