Mary,
When I had my 20 with the tapered comptip, the advice I had always heard was to get on the righting line ASAP after a capsize, because the tapered shape of the comptip didn't have as much bouyancy. The few times I did capsize that boat I followed that advice, and it did indeed feel like if we weren't on the line quick it would have turtled. Since I never put the comptip on my 18, I can't compare directly there, but the 18 with the solid aluminum mast (not tapered) felt more stable on its side than the 20 did. My 6.0 (fairly decent sized section, no taper) feels solid as a rock after a capsize, granted I've only done it twice. Out of the three boats, the 18 seemed to take more effort to right, with the 20 next, and the 6.0 the easiest.

With respect to the 20 comments, I think the difference is because of the tapered shape, not the fact that it's a comptip.