Now the all monitors don't really count, unless they are getting power through the PC, which I have never heard of. They all have a power cord to a electric socket, correct? If so (its got to be), then the monitors won't be taxing the PSU.
The current system could run fine on a quality 400W PSU. Most bad quality PSU run at about 70%. A 80+ PSU will run at 80%+ (Source
Now the PSU you buy now depends on the that you are going to get. Like even GTX 780 Ti SLI can run fine on a 80+ 750W PSU.
Also, while looking for a PSU, you should go by this very useful list. http://www.tomshardware.com/answers/id-1804779/power-supply-unit-tier-list.html