I have the same machine. My rotary table (very old, branded “Ace”) is 6″, and I find it it annoyingly small. I reckon 8″ would be do-able if you can find one that isn’t excessively tall. Note though that I’m talking about using the RT flat – if you have one that can stand on end, then 6″ might be about the biggest you could use. I’d favour the ease of setup, clamping, etc., with the larger table, over the stand-on-end capability.