Yes, Sultans are showable. They aren't common at shows and fairs, so they're always a sight. I'm hoping this year I run into a few at my upcoming events.
If you keep them in good condition (cleaning up their living space regularly, feeding them a proper, healthy diet, fresh water and constant check-ups for health, etc.) they're a great choice for showing, IMO. Quality is a problem, as I have yet to find a breeder near me. Personality-wise, the breed is VERY docile, quiet, and reserved. They work very well with their owners, even better if they are hand-reared. I find Sultans easier to handle than other crested breeds, though I'm biased because I haven't had the opportunity to work with many.
Only faults I've had are that they don't do well with more aggressive breeds, such as the egger-breeds (generally), and game breeds, or really active types. They also aren't too hardy. My pullet under this post got sick 3 times in her first few months. With a little TLC, she became better. It was only a little cold, but if their being prone to illness is the worst of their qualities, I still find them a great breed.
My pullet, at about 3 months old, if memory serves.