I don't know what the hard upper limit is. The "400hz" estimate is necessarily rough, because the line isn't well defined. It depends on how much stuff the tracker is doing every frame, i.e. how many macros are currently in use, how many notes you start or stop, whether vibrato is on, etc.
I only found the limit because I was testing a fast-forward feature for MOON8, which I think was topping out just over 8x speed, i.e. 480hz. It was rough though, some frames I think would run too long and cause a skip (not an issue for a fast-forward feature, but if you want smooth playback it would be a problem).
Also the "maximum" speed shouldn't have anything at all to do with 60hz or multiples of it. There's no reason for that.
I dunno, when I track at faster speeds than 60 Hz I like to think "this speed is exactly 5 times 'normal' speed". If the upper limit in Famitracker should be arbitrary, 420Hz or 480Hz would be decent numbers to go for I think.
But whatever, it's not an important issue to be discussing, let alone in this thread. :)
I am going through a difficult and unexpected period in my personal life. I'll try to compile and post the results as soon as possible. Worst case scenario, FT 0.4 goes online and the final demos get added in later. I apologise for the inconvenience.
#10 is amazing on a technical level due to its using the FDS modulation to produce actual FM. It's also above-decent musically. Of course, that doesn't mean that it necessarily surpasses every single entry in the pack. It's all subjective, you know... :)
Also, #10 used one wave that's actually 2 sounds in one. Well, a tri with its parallel octave.
And I'm not sure if the composer was intentionally making FM that phases crazily or just didn't know that you pretty much have to tune each modfreq to one that phases very slowly.
Regardless, top notch tech in the FDS, and ballsy 2A03 @ 400hz tech.