I wouldn't be surprised that the longer time and larger amounts I used helped make up for any reduced extraction at the lower temps. I'm pretty sure that there are several variables at play here.I just tapped my "Double Whirlpool IPA" last night. It still needs some time to finish carbing up, but the initial sample seems quite promising.
I brewed an IPA using only two hop additions. The initial one was a 60-minute flameout hopstand using Meridian and X-17. The second was after cooling to 120F, with a 60-minute hop stand using Vic Secret and more X-17. Since the three hops have rather distinct flavor and aroma profiles, it's easier to pick out which each addition is contributing to the finished beer. In particular, Vic Secret has a big passionfruit character that neither of the other hops has.
I was very pleased to find that the finished beer has a massive passionfruit aroma. I'd need to do a side-by-side to see how it compares to dry-hopping, but at the rate I'm using (5oz in 3 gallons for the 120F whirlpool, 1 ounce of which was Vic Secret) I'm pretty happy with the amount of aroma I'm picking up. I'm tempted to start whirlpooling at 120F instead of 170F for beers where I don't want IBU's from the late hop additions based on this result.
Good info. I may do some tinkering. I stopped steeping below ~ 160F because it seemed there was a bit of drop off in aroma, at least in my mind. So I arrived at 170-175F as my preference. May need to revisit soon. Thanks.