FYI to answer the lift discussion and deep wheel stability question, its 2 part:
The sailing effect if the X component of the lift force that is generated by the flow interacting with the bluff body (wheel). Lift is the force that is perpendicular to the angle of attack. Due to the shape of the wheel, since it is symmetrical, lift and sailing only occurs at yaw angles =/=0. Once you have an angle of attack that is non-zero, the lift is generated as the flow of the air is redirected due to vortex shedding and lift is the result. Since the lift is perpendicular to the angle of attack, the x direction force with respect to the wind (or a stationary observer) will be a small portion of the generated lift. The more angle of attack and the higher the lift, the more “sailing force” will occur (higher x component of the lift).
Part 2 is flow stability. As you go faster (or the wind goes faster) fluid attachment to the bluff body will eventually un-attach and then you will see stalling occur where the flow will not be redirected and lift ceases. The twitchy nature of the front end comes from the violent attachment and un-attachment that occurs and basically oscillates the wheel; the pressure differential is an observable result of this phenomena. I should note that its not the magnitude of the “pressure differential” that is the issue, but the constant fluctuation of attachment and un-attachment (or swings in pressure changes) that cause unpredictability and twitchiness. Fluid viscosity (temperature, air density, air makeup etc.) are all things that affect how the fluid behaves, along with the more important wind speed, wheel/bike speed (AKA speed of wind with respect to the wheel), angle of attack and bluff body shape (wheel shape). So, one deep wheel will not perform the same as another, and in different angles of attack and wind speeds you could see huge variations on stability and sailing.
Ultimately you are trying to keep the wind attached to the wheel and minimize the amount of violent un-attachment and reattachment that occurs when the wind “slips” off the wheel and stalls, and then reattaches. As you go deeper, the lift typically increases and as a result, sailing also increases. Unfortunately this also increases likelihood of stalling (flow un-attaching) and therefore instability of the rider. Some wheels are designed to be stable in a variety of conditions, and ultimately you would want to pick a wheelset that maximizes lift while also remains stable. Deeper does not always mean better, and some deeper wheels are more stable than others simply due to shapes. Shallower wheels will trade the lift generated for more predictable “twitching” and overall stability.
Hope I answered the topic as best as I could. If there are any actual expert experts out there feel free to chime in.