Sintereds in the wet conditions will well outlast organics & I've not seen any real loss of 'bite'. Goodridge seem to be way better than the Shimanos so they're worth the extra IMHO.
Generally speaking, it's unlikely to be pads that cause squealing unless they're contaminated with oil or summat. There are unfortunately many other possible reasons for that :)
I was told years ago by LBS to fit new pads & do six or so sprints/stops to bed pads in - not had a problem since
yeh tom organics dont build up as much heat as stintered but vanish in the wet... had goodridge organics on my I-drive last summer and they lasted fine but one wet ride in dalby killed them.
Saying that XT's are ment to be well insulated from pad heat..