I have an application that will have three, 12 inch pcbs connected via pin header connectors.
Three signals will be passed from one pcb to the other two. Trace length will be 30 - 36"--pretty darn long.
I have series resistors at the signal sources to slow the signals down, if necessary. The series resistance probably will NOT be necessary, since the signals are driven by an ATTiny.
I also have a series RC network at the receive end, to match transmission line impedance, if necessary.
Two of the signals are I2C and maybe driven from an external controller. The other is a 50 Khz signal, but the faster the rise/fall times I can get, the better, since the edges provide timing info. Slower edges will mean I'll have to worry more about phase jitter.
There's plenty of space on the boards, so I can make them wide Up to about 30 mils), if wide is better. But, while wider means less series inductance, it also means more capacitance.