Joe,
I spent considerable time looking at both Vertical and Horizontal sumps.
To start the Horizontal sump is more expensive. The performance advantages are its positioning makes ram air easier to build in.
If you are not married to the idea a a smooth lower cowl there are alternatives to the serpentine duct from VAN's. Rod Bowers is one example of a Ram-Air duct system that incorporates an inlet just below the spinner.
The vertical sump is easier to install. Using the scooped lower cowl will accommodate either carburated or injected induction with very little difference in hardware.
For me it came down to: What is my mission and how much time and money do I want to spend chasing horsepower? I decided to save some time and money and use the vertical intake. It has worked very well.