Mechanical fans(single vs single) will almost always pull more air then electric. There are exceptions. But they are not cheap. Dollar per dollar the mechanical will keep that engine cool better while costing a very marginal hp difference.
I would play around with seeing if you can fit a 7 blade (6 if you can not fit a 7) fan from a 80's Chevy truck. The 7 will blow your hat off and you can hear it when the thing is actually turning.
The fan/clutch can be picked up at a junk yard and unless you have a electric water pump will bolt right up. The clutch can be checked for good operation with a heat light. Once again you will hear when it comes on and watch the gauge drop in "parade" traffic. A new clutch can be bought for cheap and bolted on quickly if the junk yard one is not turning on/off when it should.
But, you asked about electric fans.
I prefer to run 2 small fans vs one big fan. I have even run 3 before. The reason is that you can cover more area with 2 or 3 small circles then you can with one massive one. A shroud pulls the air towards that one fan. But by having 2 or 3 you have that blade right there already. With 2 or 3 fans you can also set them to come on at different points drawing less amperage.
Right now I have one coming on at 195 and another turning on at 210 which keeps that temp right around 215. Both fans are using independent controllers drawing 25 amps each. It is just less strain on your alternator then placing the load on it all at once.
I am cheap at heart so I tend to hit up junk yards. My favorite fans are ones without shrouds from the factory.
OK I have not taken a picture of the ones before I cut them up. All I have is a video. But what you are looking for is the factory fans that have the ring(shroud) around the fan blades. Or (my favorite and in the video) where the blade is actually curved.
The ring is good. But if you can find one with the "lip" that little lip pulls air in from around the fan itself.
Here is a ring from a lumina.
http://ecx.images-amazon.com/images/I/511vf77Qt+L._AA250_.jpg
Here is a ring from a grand prix.
http://i.ebayimg.com/00/s/MTIwMFgxNjAw/z/5i4AAOSwIgNXqNZw/$_1.JPG
Here is my favorite fans. The actual blade has the ring with the lip that pulls more air around the fan blade and the picture below is almost what you will find in the junk yard. The metal piece is replaced by plastic.
http://www.wright-here.net/images/olds/electric_fan/fans-1.jpg
Electric Fan Installation
You can cut these down and melt the corners together to fit most radiators. I have laid them vertically, and horizontally(in the video) to fit them in almost anything.
The motors are tough. I have abused them through water, ice, sand, they were made to last. If they do go out they come out easily. Hey its a stock part so your not looking for a company that may have changed hands.
Here is my current project(one of 4 ongoing) just to show you the fan/blade that I am talking about more then anything.