only the 980/990 have alloy carriers
weight is the main difference
950 weighs about 450g (11-34)
970 weighs about 400g (11-34)
980 weighs about 310g "" ""
990 weighs about 300g "" ""
if you're a weight weenie Shimano are lighter par for par
Deore about 400g (11-34), Sram 950 equivalent
SLX is about 315g, Sram 970 equivalent
XT is about 300g (11-34), Sram 980 equivalent
XTR is about 245g, Sram 990 equivalent
If you're using a Hope ProII hub you need to use an alloy carrier on the cassette (980 or XT and above)