I'm getting ready to brew an all grain 9.5% double IPA. I normally almost always boil for 60 minutes, but some research has indicated that for bigger beers like this, more water from the mash to start may allow for more good stuff from the grains to get into my wort. Then a longer boil time to get down to desired 5 gallons. Is this accurate?
A lot of big beers get thier high OG from boiling off water since there is a limit to grain extraction.
For example a Wee Heavy can require a 3-4 hour boil.
Check your recipe and make sure it doesn't rely on a long boil for the OG.
IMO you can't go wrong with a 90 minute boil just for DMS reduction.
Not really. A longer sparge increases the likelihood of astringent grain flavors. Yes the longer the sparge the more you get out of the mash, but there is a trade off between more and more of the converted sugar (efficiency) and the extraction of more than sugar in the form of astringent compounds.
It is true, that if you collected more water then yes you'll need to boil longer to get rid of the extra water to hit your target OG.
The most maltier flavored beers come from using a bigger mash (more grain) and less sparging. Its a sacrifice of efficiency for sure. In general, I have found in my own brewing that doing a bigger mash with less sparge create richer flavored worts. I have heard this talked about on podcasts and seen it in print in a handful of places too. (Which is why I tried it).
Overall, its best to plan a mash that gets you to your 9.5% target in a normal way. Not trying to stretch a standard mash to get more.