We test drove both a non-adaptive and adaptive suspension Z4 back in 2009. The difference was significant and steered us to the latter as a 'must have'. Both cars had 18" wheels. While non-adaptive was fine, the adaptive, even in Normal mode, seemed tighter and more controlled. There is a post from some time ago on this board that graphically explains the suspension setting differences (in terms of stiffness) between the two, and shows that the adaptive drive on Normal is actually a bit softer than than the non-adaptive suspension, but stiffens up when placed into Sport or Sport+.
As an aside, my wife insisted on keeping the stock 17" wheels on our Z4 - oops, I mean her Z4. It rides very well, even with RFTs, but probably doesn't corner as aggressively as those with 18" or 19" wheels. Cheers.
2013 535xi, Carbon Black, beige interior, M Sport package, HUD, DDC & ARS
2010 Z4 35i, Crimson Red, beige interior, 6sp manual, Adapative Suspension
2000 528i, Cosmo Black, beige interior, Sport package (retired)