dalek

hi, im new to the forum so a shout out to you all. having recently bought my 2011 xj6n, my question is what size of top box would look correct on it, and would it be big enough for a change of clothes for rider and pillion for a weekend away. also have considered givi panniers or kappa kn33 panniers but my concern is , would they get in the way of the pillions legs? thanks guys n gals