With regard to your question: "I guess the higher up the guard the hole is the less likely it is to cause problems, right?? "

I assume you're worried about water intrusion? If so the biggest concern should be rain and spray. If you're worried about getting pooped anything above the cockpit seat level is unlikely to let much water in. For rain and spray you should make sure your cables exit whatever hole in a downward angle, so water running along the cables runs away from the hole not into it. Water should drip off the lower arc of a sagging loop rather than into the hole or instrument.

BTW -- drilling in stainless tubing is difficult, especially if you are a novice and want a smooth edge. I think you should still consider routing your wire from the aluminum pedestal base.