For Gameboy clocking 3 'generations' need to be seen
- All 'classic' Gameboy, that is the original all the way including micro run (the 8 bit CPU) from the same 4.194 MHz MHz crystal, divided by two, for a CPU clock of 2.097 MHz.
- Gameboy Color and later added a double speed mode, allowing the 8 bit CPU to run at 4.194 MHz
- Super Gameboy does as well run the same CPU, but clock speed was now derived from the SNES system clock, divided by five.
Dividing the SNES (*1) system clock by five comes quite close to the original clock rate, but not exact. In addition the SNES clock differs between NTSC and PAL units:
- SNES PAL clocks at 21.28137 MHz, so the Super Gameboy gets feed 4.256 MHz
- SNES NTSC clocks at 21.47727 MHz, resulting in a 4.295 MHz clock
The resulting frequency is either divided further by two for 'normal' operation, or used direct for fast (GBA) speed.
This translates into a speed up of
- 4.256/4.194 = 1.0148 or 1.5% for PAL units and
- 4.295/4.194 = 1.0241 or 2.4% for NTSC units.
All of this is essentially without any change to game play, except for some rather offbeat usages - like doing competitive speed runs, or trying to get fastest ever runs. Here a percent up or down may result in several seconds faster or slower.
Long story short: Nintendo (and next to all users) accepted this little difference in exchange for being able to play their old games :))
*1 - It might be worth to add here, for everyone not so familiar with Gameboy generations and details, that the 'Super Gameboy' isn't a hand held game, like everyone might assume, but a cartridge for the SNES containing most parts of a Gameboy, except I/O. Instead the game output is displayed on the TV connected to the SNES, while input is transferred from the SNES controllers (which also introduces a tiny lag - that's why the next generation got an optional dedicated controller - AFAIK).