The Size menu item lets you set a point size for the text. Point sizes in the menu that are displayed in outline are sizes for which there is a screen font. These point sizes provide the best possible display quality on the screen (at 100%).
Point sizes not displayed in outline may look jagged on the screen, unless the font is a TrueType font. If so, it will look good on the screen at pretty much any point size. Text will also look good at any size if it is a PostScript font and you have the Adobe Type Manager‚Ñ¢ (ATM) installed in your Macintosh System Folder.