"Lovely" and "accurate enough to compete with David and Paul" are two different things. Recall that at the entry and exit of every corner, and the intersection of the round loops, and even the round loop entry and exit ALL require infinite acceleration to perform.
and In the real world with gravity and atmosphere, there is no such thing as "infinite acceleration"
Brett's key word is "require".
If you do the calculus on the pattern, you find that the transitions from straight to corner and from corner to corner (in the eights) do not require infinite acceleration from the center of mass of the airframe -- they only require that the acceleration of the center of mass of the airframe change instantaneously, either from zero (straight-line flight) to canopy-up or canopy-down (corners), or they require that the acceleration change from canopy-up to canopy-down, or visa versa.
So the center of mass of the airframe isn't accelerating infinitely, but it does need to generate infinite jerk (for non-mechanical types, 'jerk' is name used by mechanical engineers and physicists the first derivative of acceleration. I'll let you draw whatever linguistic parallels with the people involved in this discussion that you may wish).
If the aircraft needs to change pitch to change acceleration, however, then to follow the pattern exactly it would need to change its angle instantaneously at these transitions -- that would require infinite angular velocity, acceleration, jerk, and everything else. This would, in turn, require infinite "everything" everywhere on the airframe except around the axis of rotation. So there would, indeed, be infinite acceleration.
Even if you avoid the need for instantaneous angular displacement of the whole airframe by trimming your ship so that the fuselage angle of attack is zero in a corner (which you can achieve by fiddling with the flap-elevator ratio), you would still need to move the controls instantaneously to make the transitions.
Some people, Paul Walker among them, are very good at approximating this. If you watch Paul or one of these others fly (in a non-gale, Eugene this year doesn't count) then you can almost perceive a "click" at the intersection to the eights. I'm not sure if it's there when Paul does his square corners -- I'll have to pay attention the next time I see him fly.
So, yes, infinite acceleration is
required. And infinite acceleration is never going to be
achieved. But like the joke about the engineer, the mathematician, and the pretty girl, those of us with the right training know that you can get close enough.