S5 Pro a good choice for IR?
The S5 still has the IR cut off filter and it's just as strong as anyone's. You can try using a 87c or RM90 over your front lens but your images will still be less than good.
Any filter less than the 2 above will let in too much daylight and again, defeating the purpose and effect you desire and see by others. You may come close, but no brass ring.
If your dead serious, convert the camera, get a S-3 in IRUV or as another post here said, a Fuji IS.
Trying to - force - IR thru the camera's hot mirror makes for longer exposure times resulting in more noise and a grainy look. I know, I've experimented.
Does the equipment make the man..? No..! But it sure can make the man money...