crossfire or better card

get a single R9 280x if those are your only choices, but you can get an R9 290 for $270

http://www.newegg.com/Product/Product.aspx?Item=N82E16814161459&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
 
single faster card may not get as many FPS in benchmarks compared to 2 mid range in crossfire, but its always more reliable, less stuttering, less fps dips, less compatability issues, less artifacts adding up for overall better gaming. Ive had both sli and crossfire setups in the past and was never 100% satisified, there is always one game that doesnt perform properly, or glitches or something, meaning your putting one card to waste.