I'm wanting to try some 4 inch grubs and 3.3 Keitechs on 1/8 and 1/4 round jig heads for finesse presentations this winter. 

 

What size hook should i be looking for?

I use the 1/0 sized Owner Ultra Heads on the 3.8" Keitechs and it puts the hook right at the end of the slot, which I feel is ideal to keep the action at low speeds.  I have also used the VMC Rugby heads in 2/0 and they put the hook in almost the same spot.  

I feel like with jigheads, there is even less consistency across brands then with hooks and you have to look at each different one to see where it puts the hook in relation to the plastic.  But I suspect that you want to start looking in the #1 to 2/0 range.  

I assume that you are talking about the Keitech - Fat Swing Impact 3.3 bait. Rig them on a 1/16 0z. weighted twistlock hook, swim them slow, fast or on the bottom.

Outkast Tackle Money Jig 1/8oz

Owner ultrahead Round jig head. They wont let you down.  They have 1/8 Oz In a 2/0 hook, 1/4 Oz in a 3/0 hook.