Hi Colin,
To some extent, it depends on what you envisage doing with your Ward indexer rotary table.If you
are going to be using it mounted horizontally for e.g. drilling holes on a pitch circle or machining arcs then I agree with Chris, go for the larger one. If you want to use it in a vertical sense for example to cut gears then you need to ensure you have enough operating room under the cutter.
One small consideration is the worm wheel ratio that determines resolution. The larger tables tend to have 90:1 ratio while smaller ones have less resolution e.g. 72:1 or 60:1. However, in practice, it won't make a lot of difference.
I have motorised my Myford badged HV6 rotary table and use it in the vertical position under the KX3 CNC mill. It works very well but the biggest problem is getting the table from the mill stand cupboard to the mill table! It is a very heavy unit which led me to put a stepper on 4" ArcEurotrade (no connection) rotary table as it is so much easier to manhandle. Another advantage is the body is ground on all faces of the body which makes tramming it in the vertical position much easier.
You have made an excellent choice building the Ward indexer (no connection), it is a superb design that works flawlessly.
LesT