XT 761 is the 2004-2007 groupset
XT 770 is the 2008 onward one
Although the total weigh for an XT761 22-32-44T is claimed at 860g and SLX 22-32-44T is claimed to be 889g (XT770 22-32-44T being 853g), the XT arms are heavier than the SLX ones (I weighed them)
XT761 and LX rings are made of aluminium and wear out quite quickly (made of cheese)
XT770 and SLX have a part steel middle ring (the teeth) (lasts way longer but heavier) and part 'composite' (the part that connects to the crankarm spider. (SLX double/bash has an aluminium 36T ring I believe). Inner/outer rings are aluminium but I reckon (just my experience) are longer lasting than XT761 and LX chainrings
As above the 48-36-26 rings may tip that crankset over the weight of the SLX too
Go for the SLX