Two of mine were as big as Ski mentions, but one split and the other hasn't been that big for a while now (but it is recovering daily). Rapid swings in DOC and perhaps even cotaminants from several ice cubes I used to attempt to move one that was causing trouble, to say the least.
Moving it turned out to be an incredibly stupid decision, as while still healthy, it has been in hiding for weeks now and is beginning to bleach. It is not unheard of for Bubble tips to hide until they bleach then come back out and colour up, so hopes are still high for the hider. One half of the split is still hiding as well, but he still gets a bit of light.
As for compatibility, mine regularly expand to the point of touching corals, but cause no harm. The polyps don't even retract.
Finally, as always my recommendation for captive bred bubble tips (Entacmaea quadricolour) to be the first choice in symbiotic nems, and for un-bleached Heteractis crispa, Stichodactlya haddoni carpets, bubble tips and Macrodactylum doreenensis to be the second choice.