I use 20'+ MIDI cables on my remote keyboard. No problems at all...

I find making sure the MIDI cables don't run alongside power cables, and computer peripheral cables, lighting control cables, or anything that puts out an interference field has more to do with long length reliability, other than the usual stuff of making sure it doesn't get kinked or pulled, and using decent quality cables (anything other than rock bottom ones, in other words), than anything else.

I can't even remember the last bad MIDI cord I had...

Bernie's problem sounds nothing to do with the cable, if, as he said, he's already done the same thing with a G70 and had no problems...