I haven't heard the Legacy speakers you mentioned. Since you said you liked the W/P 8, I thought it might be desirable to identify the differences with the W/P 6.
I guess Wilson would say that the W/P 8 is the latest and greatest. Since the W/P 6, Wilson has changed the enclosure material, tweeter driver, and the crossover. (At least, these appear to be the major changes.) The result seems to be a softer high end, smoother midrange, and a woofer that goes a little deeper but no longer has the slight mid-bass prominence that contributed an illusion of better bass.
Conversely, the W/P 6s (and earlier versions) have been criticized for being a little hot on the high end (analytical? strident?) and having the mid-bass bump and not going deep enough on the low end. Sound wise, the W/P 6 sounds a little "hifi-ish" (West Coast sound?) with a slight emphasis on the frequency extremes. I have the W/P 6s, and they sound fine in my room, which is furnished and configured in a way that tends to mute the highs. I also have two subwoofers strategically placed and crossed over so as to fill in the bottom octave. This last is a real plus when I use the system for home theater.
Bottom line, I would recommend you listen to the W/P 6 yourself, if possible. It is a different speaker from the W/P 8 that you liked. Depending on your tastes, you might still like it better than the Legacy.