Does resistor choice for I2C with optical isolation depend on voltage or speed?
The second diagram should work, the text says up to 400kHz and not for only 400kHz. Also the only thing that limits the speed is the opto-couplers, which on the datasheet says its maximum data rate is 15 Mbps, which is good for 100kHz.

Also the 390 ohm resistor is only used as pull up resistor, as this is  connected to a transistor collector. As for the 180 ohm resistor, it is used to limit the current that's flowing into the diode. The change in resistors in both diagrams is only because an increase in voltage would increase the current, so resistors should be increased to stay at current limit.