I've never subscribed to wider trucks for quad vert. We have the equivalent of two boards supporting us so horizontal stability isn't an issue unless you skate crab-legged...which looks stupid anyway. Just running hardened axles to take the impact and softer durometer wheels has worked just fine for me. - my 2 cents.
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If the good Lord wanted us to walk he wouldn't have invented roller skates." ~Willie Wonka 1971
60 secs of Quad Vert Fun 
link:
http://www.youtube.com/watch?v=dYJgY2PJ_vk