The two factors to play off against each other are the size of job you may work on and whether the RT will be awkward to use on the machine, any loss of axis travel or daylight may be annoying but can often be worked around. Mounting a large job on a small table might be even more difficult, of course the job will always come along that is too big no matter what size RT you have. I would go for the 5 inch as overall I think it would make life a bit easier, remember you need to hold the job on the table somehow and the larger table leaves more room for clamping.

Mike

I've used a 150mm one on the SX2.7 quite happily, the only time you may run into issues is if it is mounted horizontally with a large 3 or 4 jaw chuck on it and you are using a drill chuck and largish drill bit. Not had any problem milling items mounred directly to the table or in a 3-jaw.

Edited By JasonB on 29/09/2020 11:51:05

I have a Soba HV6, on my SX2.7 it's fine using it horizontally, but vertically the mounting slots are too wide apart for the table t-slots. I've not needed to use it vertically yet, but I'm sure a clamping arrangement can be devised.

I bought a 6" Soba RT which has horizontal and vertical with four tee slots. The vertical position needs clamping down on the mill drill, but the Tom Senior slots are just right. In the vertical position, I was concerned with its stability, and have drilled and tapped a pair of 8mm in the base to bolt on a small angle plate which can be clamped to the mill bed. I would go for the largest that you think will fit your machine, 5 or 6 inch diameter.