What you want to do is take and add up all the wattage that you will be connecting to the UPS and then look for one that will supply what you want.http://extreme.outervision.com/psucalculatorlite.jsp http://images10.newegg.com/BizIntell/tool/psucalc/index.html
What is your budget amount for the purchase of this UPS.
Based on the power suply calculator your main Pc will draw abot 375w and that's not counting the two monitors. I couldn't run the work Pc because I don't know the specifics.
It's looking to me like your needing a 1000w UPS and after looking on Newegg those are somewhere around $600-$700.http://www.newegg.com/Product/Product.aspx?Item=N82E16842111144