D47 is not real sensitive to pH. It is actually pretty good about fermenting to completion even with a pH of less than 3.0 (but it needs enough nitrogen and potassium to do it). Although it isn't considered a nutrient hog, it does perform better if you provide proper nutrients, and while that might be said of many yeast, it applies even more to D47
The book you were reading was probably the old Acton and Duncan's Making Mead book. I saw that reference and it inspired me to include Tokay in some high temperature testing. When fermented in the mid 80s F, it tasted poorly and was slow to clear. In the book they report the individual who claimed it worked well said you needed it at 95 F. I plan to test in at 90+ F, perhaps this summer if I have the time.
I can tell you that EC-1118 is a poor choice for high temperature fermentation. Yes, the yeast can survive and ferment with no problem, but the odor and tastes that are produced are simply bad.