It isn't clear to me that coils ALWAYS fail at any rpm when they go bad. I've seen multiple sources claim hot temperatures can affect spark delivery when the coil deteriorates. However, you're right, when they absolutely fail, they do fail absolutely.
As an example of how coils can degrade: on one of my other machines, a 1997 BMW R850R, the coil is basically a square plastic cup that houses the circuitry and the manufacturer poured red epoxy into the cup to seal things off. Over time and heat cycles, the plastic outer shell will expand away from the red epoxy center, allowing air and moisture to leak in and corrode the electrics inside. That bike would, at a hot idle, stumble every few seconds, but on throttle it always ran great at any RPM. This was just the beginning stage of what would eventually (probably years later) have been a complete failure. I replaced that coil and the idle is now very smooth.
Brett, I think you have a carb issue. At least one of the four slides isn't rising or at least one of the carbs is not getting enough fuel through a clogged main jet at higher RPM's. I can't think of a single thing in the cylinders or valvetrain or even the spark system that would prevent the bike from revving out past 6k. None of those things are RPM-dependent on this machine.
Unfortunately your issue is combined with known-low compression, so you have a choice to make. You can remove only the carbs and figure out what's going on inside them, or you can pull both the carbs and the engine out and do the top-end work. Up to you. With low compression and properly functioning carbs, you could simply keep riding until the bike is so slow you can't stand it and then yank it open to do new rings.
I tested my ignition coils this morning.
Coil for 1&4: Primary 2.5ohms
Secondary (cap to cap) 22.5k
Coil for 3&4: primary 2.7ohms
Secondary (cap to cap) nothing
The bike does run on all cylinders so I need to measure those coils again once the bike is warmed up.
Tried to upload a short video of what it is doing but the 15 second file was too big
If you measured the coil between 3 and 4 then of course you'd get no ohm reading as those two aren't connected. Make sure to measure between 2 and 3 and don't be afraid to push the multimeter probes in there a little harder to get past the rubber end. You should see a brass terminal inside the spark plug boot and that's what you need to touch.
I feel like a freak when reading internet motorcycle forums -- I have not once had a serious it-won't-start-or-ride carburetor issue on any of my multiple carbureted motorcycles since I started riding 6 years ago. On every bike that's new to me I either rebuild the carbs myself or have receipts on hand to prove a professional did it. Then, I do two important things: one, I always treat the gas in the occasional-use machines with Sta-Bil; and two, I refuse to let them sit for long periods of time. You will never have "endless carb nightmares" if you ride the damn thing at least once a week or two, are mindful what kind of fuel you're putting in, and do the prudent things before storage (
draining the carb bowls!).
The only issue I ever had was starting my GS500E after it sat for 9 weeks because I broke my ankle crashing it. It had ethanol gas in it too. It started, but it didn't run very well. I threw some Seafoam in the tank and limped it around on a ride and it got better and better as the miles ticked by, until about 100 miles in it was running perfect again.
Nowadays I'm spoiled by my fuel-injected BMW's but the vintage 4-carb Honda is still around and still running strong. Learning how to fix fuel injection was a whole ordeal in itself, but that's a story for another time...suffice to say I prefer carburetors even now that I've owned two fuel-injected bikes.
