Talking two doors (coupe or convertible) one thing I find is that the shorter wheelbase versions (Catalina and Canadian) cars have nicer proportions than the Bonneville long wheelbase cars.  The extra wheelbase pushes the rear wheel opening back.  On the 4 doors it is fine because of the longer roof area but the 69-70 roof area on 2 doors seems smaller and the rear axle looks too far back from the roof area.

I don't have a 2dr hardtop Bonneville and I couldn't find a good picture of a 69 so here is a 70 which is identical apart from bumpers... 

The shorter wheelbase Catalina (or Canadian) looks balanced...

But the long wheelbase Bonnie looks a little off balance...  I know it is only 3" but I see it a mile away.