Depends on how much time it takes your music code to run. If FamiTracker takes 10% of a frame to run, then about 600Hz is going to be as fast as you could update before it breaks down. If you put it to 1000000Hz there's probably not even enough time for a single instruction.
Here's what I was originally working on for my WC7 entry. It's just a skeleton and some drafts of ideas that never fully fleshed out. The aim was to make an arpless 2a03 jazzy prog tune.
I put it down mainly cos I just wasn't feeling it after a while and didn't think it was worth the effort to tie all these parts together...so I settled on making that poopy dungeon tune -__-
edit: also cos I need to focus more on learning more nes techniques instead of churning out song after song using the same approach.
Here is my soundtrack (31 songs max. 3 frames ) and a motor.
Don't mean to be rude, but this soundtrack isn't actually that good. Though, it does sound like it came from one of those bad games with bad soundtracks where some of the songs are quite catchy. I don't know if you'll take that as a valid compliment or not, but hey... I'm just being honest. :P
EDIT: Here's an edit of a module I saw in this thread earlier, by a guy called Ares64 - I liked it, so I did my own spin on it using only 2A03, as his was in MMC5. Enjoy! :D