I would agree with Thor, Harry, the larger size may be usefull on occasions, keep it and use it. Most users of a vertical slide will I think agree with that having occasionally wished their slide was larger.
The Vee slot may be useful on occasions but a problem on others when securing small parts using table clamps. However, I think this could be overcome by some meens when the problem surfaces
I would though advise that you use a toolmakers style vice as these give much greater flexibility as to where they can be positioned. This includes vertical or horizontal, or any angle between.
See Photo 4 here for an example**LINK**
Comparing this with Photo 5 should show the benefits of using the toolmakers style vice. The toolmakers vice is also likely to have a larger work holding capacity.
Harold