Если нормально сделать, то i2c можно раскочегарить на 40+ метрах (и даже больше). В PS/2 протокол похожий

> When the keyboard or mouse wants to send information, it first checks the Clock line to make sure it's at a high logic level. If it's not, the host is inhibiting communication and the device must buffer any to-be-sent data until the host releases Clock. The Clock line must be continuously high for at least 50 microseconds before the device can begin to transmit its data.
> The keyboard/mouse writes a bit on the Data line when Clock is high, and it is read by the host when Clock is low.

Т.е. скорость передачи может быть почти любая, независимо от инерционности линии. И хост и девайс подстроятся под скорость изменения (если грамотно сделать всё).