My 2010 Ibis Mojo finally needs a new cassette (and chain)...I'm considering either the xg-990 or the xg-999 to replace my existing xtr 9 speed. There is a big difference in price ($70 vs almost $200), and so far all I can find is that the 990 weighs 95 grams more than the 'made from one piece' 999. Are there any other performance differences between the cassettes that I might notice, and will I notice the weight gain? Thanks.