As long as the cable is short enough that interference doesn't corrupt the signals, either it makes it or it doesn't -- it's data, not an analog audio signal. The extra length might cause there to be a difference in nanoseconds in the time it takes the messages to stream down the cable, way way smaller than the resolution of the MIDI interface and hence negligible.
I think the MIDI spec has a maximum cable length in it, but I don't know whatit is.