I actually never had any trouble with Flirtin' With Disaster. IMO it's probably the easiest final tier song in RB1.
I will probably sound dumb for saying this, but... What is Break-Neck-Speed?
Breakneck Speed is one of the options in the modifiers menu, if I remember correctly. Been a while since I've looked at the RB1 menu. (What system are you playing on, BTW? If you have a 360 you can get RB3 from games on demand for pretty cheap, and import RB1 for $5, and RB2 for $10 if you have an unused import code)
Basically, it takes the speed of the game up one or two settings from the difficulty you're on. So if you're on hard, BNS is basically like playing on expert for the speed of the note chart, but still with the notes from hard. If you play on Expert + BNS then it goes REALLY fast. It's useful for songs where there are lots of notes densely packed, so that you can see patterns more easily, but you see less of the song at once. (It doesn't change how fast the song actually plays, so to move the notes faster it just makes them more spread out.)
I have some friends that HAVE to have it on to do well. I use it occasionally if there's a really dense part and I'm having trouble reading which notes are simultaneous and which are offset slightly. (Though I mostly just drum) I like it for playing on Hard on a song that I just can't deal with, like Through The Fire And Flames. I'm so used to the speed of Expert that when I play on Hard it throws off my timing, because I'm used to the notes moving at a certain speed.
It could actually be a good way to go from Hard to Expert. You could play the songs you're good at on Hard + Breakneck speed, and then when you switch to Expert + Normal Speed, all the notes will be moving at the same speed as you've just gotten used to, but there will be more of them.
Also, if you're playing the devil-tier songs on Hard, you are more than capable of playing anything at 4 dots or less at Expert already, probably. I find that the tier rating of the song is a better indicator of difficulty than the actual difficulty setting, once you get used to playing using all 5 (10 if you use the solo buttons).
One thing you may not know is that any of the HOPO stuff is like the regular buttons, in that you don't need to let go of the lower notes to hit the higher ones. So if you see a blue->orange switch, you can keep blue down and tap orange. That works for yellow->blue->orange as well.
You can do that with the pull offs, as well. Start by holding all yellow + blue + orange, and then an orange -> blue -> yellow sequence is just a matter of lifting each finger.
Also, practice alt-strumming. Find any song that has a consistent rhythm (or just play bass on expert) and practice strumming by strumming up and then down instead of trying to constantly strum in one direction. This will help a lot when you start playing really fast songs, or songs that throw in a few quick strummy bits. It'll keep your wrist from trying to kill you.