What type of exhaust ventilation is best for attic

There are solar-powered gable fans - an Air Vent-brand fan can be picked up at Lowe's for just over $200:

The solar panel is on a cord, so it can be installed in the most sunny area while the fan sits in the gable.

From the Air Vent website:

The Gable-Mount Solar Vent is an exciting alternative to traditional attic ventilation. That's because it is powered by a solar panel that collects energy directly from the sun and converts it into electricity -- naturally -- to power a durable, high efficiency 24-volt DC motor. As a totally solar-powered solution, it's also environmentally friendly.

Painless Installation
The best installation feature is that the fan requires no electrical hook-up. That means no electrician and no complicated wiring is required, making the installation of your attic fan fast and easy.

It mounts in the gable end of the home, behind a decorative shutter (not provided, see below). The solar panel comes with brackets that allow for mounting on the roof.

Smooth Operation
The solar panel collects energy throughout the day under direct sunlight and converts it into "free" power to operate the fan -- providing ventilation during daylight hours, when it's needed most.

It creates up to 800 cubic feet of air movement per minute to remove uncomfortable heat in the summer and damaging moisture in the winter. And, the solar panel is wind-, hail- and impact-resistant to stand up to the elements.

Specifications

• Moves up to 800 cubic feet of air per minute
  
• Solar panel collects and delivers power under direct sunlight during the hottest part of the day without electrical cost
  
• Wind-, hail- and impact-resistant solar panel
  
• High efficiency, durable 24-volt DC motor
  
• 5-year limited warranty

_{(source: airvent.com)}

Model #SHT15W

• Plastic
  
• Sold in the color white only but it can be painted to match a home’s exterior
  
• Automatically opens when the power fan is running and then closes when the fan is not running
  

For the 50:50 rule, I don't see the ridge vent becoming an intake unless there is another second ridge vent. So given the choice, I'd ignore the 50:50 rule unless your ridge vent is not at a single height.

That said, in your specific situation, with a strong wind from one side and the soffits closed on that side, I think you're creating a situation where regardless of how big the ridge vent is, you could get a down draft from the upwind ridge vent to the downwind soffits. But more importantly, by closing some soffits, you are reducing the airflow under part of the roof. In areas of heavy snow, this airflow is critical to prevent heat from the home from melting snow from the upper part of the roof and having it refreeze on a lower part, forming an ice dam that would backup water into the roof (rot) and possibly into your home (leaks).

Because of the ice dam risk, I think you're better off going with shirlock's earlier suggestion to rely on the Styrofoam tunnels stapled to the rafters and adding some ridge vent filter to any soffits you are worried about. Then install a ridge vent of the proper size for your roof.