I look at hook size being dependant upon driftbobber size and technique.
- with straight bait #4 or #2&#4, usually in tandem either way.
- raggs, 1/0 or 2/0 depending upon size.
- worms, usually 2/0 (4" and larger).
- corkys, size approx. 1/8" gap larger than the drift bobber.
- plugs, as big as I can get away with, as long as it doesn't effect the action.

That is my "system", it may not be the best, but it works for me.

Note: My experience has been larger hooks driftfishing usually equates to more LOST fish.