I found a possible reason for the slow menu display: I had a flickering screen after an update and corrected this by setting
$ xfwm4 --replace --vblank=off &
as @kommuni recommended in Flickering screen after 4.1 update. This seems to be the cause for the slow menus. Changing the vblank_mode to xpresent corrected this problem for the main menu and somewhat for the submenus. I have updated my post on this.
With regard to the start button: As far as I can reconstruct it, QWT cannot display the round Windows 7 default start button. But if this button is changed to a rectangular button, as can be selected by Classic Shell, it could be displayed.