hi,please help me,I want to buy a graphic card,and I'm stuck between crossfire4770 or a single 4890,and I dont know which one is better and faster,help me,I want to choose wisely,if crossfire4770 is better than a single4890,then I prefer to buy two 4770 and use them as crossfire,but if a single 4890 is better and faster than crossfire4770,then I prefer to choose single 4890,please help me.