I know I have on expert guitar. Before RBN began, I finally 5 starred Thrasher which completed my personal goal of 5 starring every song in every GH/RB game (minus Eruption on GHVH) on expert guitar(granted, I didn't have the entire Music Store library, but I did have every song rated challenging or higher so any song rated lower that I didn't have, I'm sure I'd 5 star with no problem if I did have every song). Them RBN came out. I did pretty good with the first wave of hard songs. Then came more Evile tracks, then the Exodus track. I'd pass all of them, but couldn't come close to a 5 star, in fact I had a hard time 4 starring some of the Evil tracks. Then Guitars SUCK came out. For the first time since I passed TTFAF and DWDTG for the first time in GH3, I had a hard time just passing a song on expert. Finally passed it once, and then 4 starred it hundreds of tries later. But it's not a song that I can just sit there and pass with no problem. And when I thought songs couldn't get any harder, then came Chaotrope. Cannot pass Baptized By Fire to save my life. I haven't been playing RB for the past 2 months because of my deployment so I don't know what kind of insane songs came out. but I saw the Diachlyon(spl) chart on Youtube and holy ****. It made BBF look like childs play.
Now that I know insanely difficult songs are coming out on the regular via RBN, I'm pretty sure there are going to be songs that will outclass Diachylon.