Pop-up vs. Fixed wall - wind performance

[Corisam]

Hi, All! Have been shopping, shopping for a Grandby or Hawk shell - no luck so far. It has seemed that any time I log some serious miles in any direction that inevitably, there are some strong head or quartering or cross winds that I always run into here in the West. Has anyone - at one time or another - owned both a 4Wheel design and a fixed wall and can offer some thoughts about actual performance differences between the two designs in winds and fuel consumption. Thanks and happy miles to all!