I've done a non scientific based experiment of the relation between sharpness/image quality and apertures.
Here's are 100% crops. Focus was on the letter "F".
ISO was constant @ISO1600. As you can notice, the higher the aperture value, the sharper the image is.
Here's a sample picture which i shot during the Comic Fiesta@Berjaya Time Square Hotel recently.Sharp don't ya think? =) I shot it @f/2.8