Karl
until I got the LN #9, I used a #6 on the shooting board all the time and it was great (not a patch on the 9 though).
In your position, I would go for the #7 - my dad was a cabinet maker all his life and he used the #7 on the shooting board form his apprenticeship onwards. #7 makes a better jointer.
According to Chris Schwarz's (plane expert and editor of Popular Woodworking) DVD on plane use, the #6 is really for 'hogging' off wood in the same manner as a jack - hence it is called a 'Fore Plane' - used before the jointer or smoother.
I now use my #6 for this purpose and it works very well in this role
If you're interested, Chris's view is 'course, medium, fine' - i.e. take thick shavings off with the Fore or Jack plane with a highly curved blade, a bit like a large scrub (6-8 thou shavings), then use the jointer (7 or 8 ) to do final dimensioning and take it close to the finished size (3-4 thou shavings), finally, use the smoother to take get the final finish with 1-2 thou shavings and tight mouth. The smoother (4.5 for large work, 3 or 4 for smaller work) should only be used for a few passes as most work is done with the other two.
Since seeing the DVD and adopting this approach, my work has speeded up and my enjoyment increased loads.