You did not say how many spokes your rim can handle. The 3 cross is stronger and would be more reliable then the 2 cross, and the weight reduction going from a 3 to a 2 cross is nil-maybe 2 to 4 grms! If you want to lose weight and still maintain wheel strength then go with a lighter thinner spoke then the rear, and lace the wheel 3x. You will loose much more weight using a thinner gauge spoke then attempting a 2x cross with thicker spokes.