I'm using the default setup in Processwire and only modified this a bit. I finally got it to remove the classes from P tags, but pasting in from Word is giving me double P tags for everything, but if I paste from a plain text it removes all my line breaks, so I cant win.
Here are my settings
theme_advanced_buttons1
formatselect,|,bold,italic,|,bullist,numlist,|,link,unlink,|,image,|,code,|,fullscreen
theme_advanced_buttons2
BLANK
theme_advanced_blockformats
p,h2,h3,h4,blockquote,pre
plugins
inlinepopups,safari,media,paste,fullscreen
valid_elements
@[id],a[href|target|name],strong/b,em/i,br,img[src|id|class|width|height|alt],ul,ol,li,p,h2,h3,h4,blockquote,-p,-table[border=0|cellspacing|cellpadding|width|frame|rules|height|align|summary|bgcolor|background|bordercolor],-tr[rowspan|width|height|align|valign|bgcolor|background|bordercolor],tbody,thead,tfoot,#td[colspan|rowspan|width|height|align|valign|bgcolor|background|bordercolor|scope],#th[colspan|rowspan|width|height|align|valign|scope],code,pre