Hi Todd,
I have printed article released by Philips 1983.
I2C bus in consumer applications
Technical publication 110.
(c)1983 Philips

Below are some snippets of the article about an I2C bus length.
... The number of ICs can be connected to the bus, and its length, are solely limited by the maximum bus capacitance of 400pF.

... The maximum number of devices which can be driven from the bus is only limited by the maximum bus capacitance of 400pF. The bus can therefore be up to 3 of 4 meters long.

... The maximum bus capacitance per wire is 400pF. This includes the capacitance of the wire itself and the capacitance at the pins connected to it.

... Masters can generate a bus clock with a frequency up to 100kHz.

I hope this is helpful for you.

Regards,
Vaclav