Drilling joists vertically

[Dave OCD]

Go through the existing hole. If you are running cables up there they would need to comply with safe zone requirements. i.e. you cant just put them in the middle of the wall unless there are accessories going on the new wall.

Just thinking about that, if you were to drill exactly in the centre of a 100mm studwork top timber you'd achieve 50mm clearance on both sides within reason once the plasterboard was fixed. I've only ever treated wiring in solid walls which is never far below the surface as the real intention behind safe zones. But having said that you can generally get a socket/switch or even consumer unit in alignment with the hole/s.

 

[pirate]

It's not a problem to drill that, and as you have a pull-cord switch there already, that will be easy to identify from above, so easy to measure from that, to the left, and avoid any joist above. Use a pilot drill before attacking it with a spade/forstner/holesaw...easy does it!