using powerful monitors in a room that hasn't been acoustically treated will probably not work out that well
Let me just change that a little: "using
any monitor
at volume in a room that hasn't been acoustically treated will probably not work out that well". There. That's better.
The bigger the room, the more volume it will be able to handle, treated or not. Bass frequencies are the biggest problem and the hardest to treat, but that doesn't mean you have to avoid them completely. Treatment also doesn't have to be a permanent fixture - a bit of plush furniture and a loaded bookshelf works wonders. See
http://ratcliffe.co.za/articles/acoustics2.shtml
+1 on the KRK Rokits, BTW