I realized that these plots are a little misleading.
The VCS3 filter is highly nonlinear and "bubbles" and so taking a measurement of frequency response is quite difficult since the filter is moving around on it's own accord all the time...!
Here is a more detailed FFT that shows how the filters do match more closely than the graphics in my paper would suggest.
.
Black is the slow accurate VCS3, Red is my optimized VCS3.
Not oversampled.
c4000_fb9_m42__one3_c050_k2.png
c10000_fb9_m42__one3_c050_k2.png
c2000_fb6_m42__one3_c050_k2.png
c10000_fb9_m42__one3_c050_k2.png
When oversampled, I found the proposed model to be perceptually identical to the slower accurate model. The resonance and cutoff values differ slightly, but the important aspects of the filter are retained.