I agree that the shroud is restricting air flow. If you look at it there is about 25% of the surface area or more of the radiator that is being blocked by the shroud. I'd either have louvers punched in it or back it away from the radiator more. Air doesn't like to change directions very well and the way it appears now it has to come through the radiator and make a hard 90* turn to get to the fan. When you are going down the road the fan actually becomes an obstacle for air flow so you need free flowing air to get by it.
Also you said you were pushing the air with the fan through the radiator. If in fact it's pushing toward the radiator then you have to change that because you're fighting any air flow through the radiator once you start moving. The way you have it mounted it needs to pull the air through.
I would advise against using straight water in a cooling system unless you want to end up with nothing but rust in the system. 50/50 mix of antifreeze is just fine (as long as it's NOT DEXCOOL). If a cooling system can't cool an engine down with that you have other problems. Not the coolant's fault.
