River has always done well since they came on IIRC, but they have been doing better since they started playing more classic rock. When they first came on, they played a lot of Billy Joel and even Stevie Wonder. I always considered the early version of River to be "AC for Guys".
I would argue that BOTH River and 100.5 have stayed away from prog rock, as have many classic rock stations as of late. They may be starting to dabble in prog rock--I heard a Yes song other than "Owner Of A Lonely Heart" on BOTH stations in the past week ("I've Seen All Good People"). Both stations have also pushed much harder into the late 60s and early 70s generally (e.g., more Hendrix, Stones, Doors, and even some Beatles), and dropped the 90s heritage rock (RHCP, Nirvana, Green Day, etc.).
The playlists of both stations have become similar, with 100.5 going deeper somewhat (more secondary hits like "That Smell" by Lynyrd Skynyrd)--although when River goes deep, they go REALLY deep.
Cox's "turn and burn" approach has generally worked well (as it did for B98.5 when they were Mainstream AC), keeping the station familiar but also fresh. It has also enabled them to throw in a few "oh wow" songs, too, without overcommitting to them or lacking proper research. They seem to be doing more turning and less burning these days.
