It is unlikely that Classic Shell is causing it because it does not affect Quick Launch or Explorer icon functionality. It may be possible that there is some shell extension installed on your computer that is causing the slowdowns/Explorer crashes. To rule out Classic Shell, uninstall it temporarily and see if the crashes/slowdowns go away. All your Classic Shell settings will be preserved when you reinstall it.
To fix crashes caused by some shell extension, use NirSoft's ShellExView:
http://www.nirsoft.net/utils/shexview.html to see all installed shell extensions. Sort them by company/manufacturer and ignore the Microsoft/built-in ones. Then by disabling them one at a time and see which is causing the crashes.