If better iso performance i'm afraid you invested in the wrong brand. Consider moving to Nikon. There d5100 is smaller and lighter. You will not notice much improvement over the 40d and 60d or any other Canon for that matter. Unless you are going full frame. Even Nikons £400 d3100 performs better than the 60d and even the 7d in low light!
http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-cameras-side-by-side/%28appareil1%29/664|0/%28brand%29/Nikon/%28appareil2%29/663|0/%28brand2%29/Canon/%28appareil3%29/619|0/%28brand3%29/Canon
http://www.dxomark.com/index.php/Cam...rand3%29/Canon