I've been fishing the Rangeley region quite a bit the last few years, and mostly with a 6wt.
There are smaller streams where a 4wt would be more appropriate, but the three "famous" rivers are best fished with a 5 or a 6
Both this year and last my best salmon came on a black ghost streamer, but well know classic fly tier Don Bastain
swears by his gray ghost wooly bugger.
The Kennebago Muddler is a local favorite too. It's basically a Hornberg with a muddler head.
Try big stone flies down deep in fast water
In May things really get rolling when the suckers spawn. I've never participated in that, but it sounds like a zoo.
Around the beginning of June, the hatches start and the black nose dace have a spawning run. The black flies are out in full force too.
There's basically the same hatches that you'd see in PA except they're a few weeks later.
Two of the major rivers are tailwaters and produce well into summer but don't expect to be alone.
We try to fish the more well known spots early in the week and then float tube some of the remote "fly fishing only" ponds closer to the weekends.
One Friday 2 seasons ago, I counted 27 other fly fishermen at the remote Camp 10 bridge on the Magalloway. We have never once seen another person on one of the ponds.
The Rangeley Region Sports Shop
has a weekly fishing report in season, and Orvis has a regular report on the Rapid River.
The Fly Fisherman magazine website has a older article on the the Rapid including how to get there (not easy) and the Lakewood Camps site has a map of the pools.
Nymphing the Big Magalloway
Beware the black flies