As long the power connectors aren't in the back you should be good, and a 7870 shouldn't be 11 inches long. If i remember right only about 9.5 inches. Thats how long my GPU fits in my lexa S
Go with this card: http://www.newegg.com/Product/Product.aspx?Item=N82E16814150606 granted it's ten bucks more, it will fit in the lexa S and there is also a $30 rebate on it