I would prefere to wear nothing at all, theres nothing more exciting then playing and thing fast while your naked. Playing arpeggios is so much more fun with no clothes on.
But seriously, unless your playing some huge concert, at like carnagy hall, or however you spell it, theres no point for a tux. I tend to like to out on the clothes i would go to a job interview in. A nice tie, a dark shirt, (or a nice white see through one if there are lots of chicks in the audience lol) black pants and maybe a jacket (purley based on the weather, but dont wear it when your playing, could be a Black Sheep Moment. hahaha,