I don't like to reuse yeast from a batch with an OG higher than 1.060 as a general rule. But since most of my beers are in the 1.055-1.065 range, I do anyway. The 1.075 IPA is definitely too high to reuse the yeast.
When I resuse yeast from a stout in a lighter beer, I do sort of a wash of the yeast. I start by pouring off as much of the stout as possible, even to the point of losing a little yeast. I then add back some cheap megaswill like PBR or Milwaukee's Best (my beer is too good to waste on this process

). I swirl this around to get the yeast back into suspension and let it sit until most of the yeast settles out and then decant again. This removes most of the color and roast taste. You lose a little yeast each time but you still have plenty left.
Wayne