First: only Madara and Izuna achieved it. Madara couldn't control Kyuubi for long even though he had EMS ( it was said during hashirama's fight) so there are some limitations to EMS mode too.. the extent cannot be told exactly since manga hasn't explained it yet..First: Obviously it matters to me since I asked it. ;___; Just curious. We'll see anyway, in future chapters I guess...
Second: Thank you!
So at this point you are free to use your imagination for the purpose of your fiction to that extent I guess... Leave a foot note if somebody is too picky around here.