With the new DX11 patch that Crysis 2 just got, running everything on max settings definitly will tear any system apart. Therefore, your best option, while a noise, hot and power hungry one, is to get another 470 and sli them.
the GTX 570 for around $300 is not going to give you a big performance increase, it will end up being the same that you have now pretty much. Therefore your best bet by far is to get another 470 and sli those monsters. Be sure, however, that you have a good power supply (750w+ will do) and lots of airflow to keep them cool.