Hard to tell without more details. Do you have any pics avail?
How big an audience are you expecting? If it's a large number, then a lot of the reverb is going to get absorbed by the bodies.
How high is the stage? What kind of restaurant is it and what type of crowd is expected? If it's an opening of a restaurant, are you playing during the meals or is it an 'after party' type of thing with dancing etc?