This is another of those personal choices and I've always erred on the side of somewhat longer skis. That's just me though and YMMV.
I've skied the Sultan in a 172 and I think it certainly different than the Mythic although not necessarily stronger. The MR is pretty stiff and has a straight sidecut making it a stellar crudbuster. The Mythic is also a ski that needs some muscle to bend at slower speeds although the shape allows pivoty turns easily. The Sultan feels entirely different. It has a lighter more playful feel yet has equal or better grip. I'd actually compare the Mythic more to a Head 88 than I would the Sultan. Keeping the short size in mind, I think the Sultan is much more nimble feeling than either the Head or the Mythic. I don't know the long term future of the Legend line but I think the MR and Sultan are targeted toward different tastes. As always, waist width does not tell the whole story.
I would characterize the Sultan as a new and improved L8K and a very tough challenger for the Watea 84. (IMO those are both very good things to be)