I run em in my Duc, gives you a fatter spark, better more complete burn IMHO. Also good to tell if your engines too lean as the tiny Electrode burns away real quick if you are, & that's from past experience :-X definately not desirable of course!
Whell i must say it's marginal if at all, maybe phsycological, but I think it feels smoother with these. But i may have talked myself into this :-/
I run DPR8EIX-9 (std Heat Range) & I also have a set of
DPR7EIX-9 (1 colder) to try, haven't put the 7's in yet, not sure if they will be of benifit, but from past experience with Street Drags, colder was better with increased HP & Avgas.