...I haven't got the jump on 2006 first flush yet...gotta get on it.
Anyway, first flush Darjeelings, which are typically more astringent than 2nd flushes, in my experience, as long as they are full leaf and not a BOP, usually I go for 3 minutes with boiling water, and sometimes slightly off the boil (205 degrees). 2nd flush I always use boiling water. It is not set in stone, so experiment as you have been. BOP's depending on how fine the leaf is, I will usually go for as little as 1 minute. Some people brew Darjeelings at lower temps because the leaves are often greenish and their tea is astringent...Darjeeling is typically black tea, fully fermented and needs to be brewed at boiling to bring out the high notes that Darjeelings are famous for...adjust time not temp. Of course if the tea is labeled Darjeeling Green, that is a different story.
The 5 minutes that you mention are typical for Chinese Keemun blacks, full leaf ceylons, and the like. Label directions for brewing used to drive me nuts too, but now I rarely pay too much attention to label directions unless it states specific directions for say a high grade sencha, which will be completely different from a typical China green.