I've recently taken advantage of White Labs switch to year-round availability of WLP090, as this rocket fuel of a yeast strain is very attenuative, very clean, fast, and floccuates beautifully. I love it.
I just brewed a wonderful double IPA (recipe is here, seriously, go brew this beer), using two vials of WLP090 in a whopping starter, and the trub/yeast at the bottom of this carboy is massive. I would have enough yeast to be set for months. Problem is, it's ~10-11% ABV (attenuated past the 9.4% I expected, I won't complain). White Lab's description of the yeast says that it's alcohol tolerance is "high", so I assume it can take a beating past the typical 13%, but I doubt that I want to push it up towards it's limits before washing it.
Is there a general rule of thumb, a safe percent of alcohol by volume for when the yeast is just too stressed to wash and re-use it?