I'm pretty sure you can tun two HD5850 on that 650W PSU. http://www.antec.outervision.com/
Also it's a pity to buy a 1680x1050 monitor for a HD5850, a HD 5770 would be fine for that resolution. You should get a full HD monitor, also good for movies.http://www.newegg.com/Product/Product.aspx?Item=N82E16824236079
Scrap those speakers if you have to, the monitor has some cheap built-in speakers you can use for a while.