what the heck is that for? I'm guessin that this is an incremental hauling system where you can pull the "pull here", reset "prusik 2" manually to keep the load from sliding backwards, reset "prusik 1", and pull again.

If I understand that correctly, you won't actually be pulling any load through pulley 2. All of your pulling load is transmitted through pulley 1 to prusik 1 - so make that sheave diameter on pulley1 as large as possible to reduce friction...you'll get no purchase advantage by sizing the sheaves differently - just a little less friction. Pulley 2 is just taking up the slack in the system as you pull at the "pull here" point - the load is moving by the load on "prusik 1" (it will be pulling with twice the force of the line you are pulling on).