Using imports from a different domains will definitely slow loading, but if all stylesheets are from the same directory speed shouldn't be a problem.
However, you don't want to have the same styles in different stylesheets as the browser should operate the last style it finds, but it may get muddled and take the wrong stylesheet first.
Try to keep the separate stylesheets for completely different parts of the page, like separate style sheets for a drop down menu or a form or just the font styles and colors.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.