good question.
if i had 100k i think i would invest more in mainstream because you never really know which site/idea/concept will make it to the ultimate goal (in my case being featured on oprah). i would def. buy with the intention of brandability instead of type in because if its a phrase or slang than with time those do change. i wouldn't put all 100k into mainstream though, have at least 20% invested in adult because it's not going anywhere.
whenever i have 100k to invest in domains i will tell you what i did with it