I have certain tables that only get written to once every couple of minutes, while being read dozens of times per second. Research has told me that MyISAM is faster when a table has disproportionately more reads than writes, or even read-only.
At what read/write ratio does MyISAM beat InnoDB in performance? Is it worth switching for me in this case, will there be any noticeable difference?
Yawn. At those rates, both MyISAM and InnoDB spend most of their time snoozing. At thousands/sec, things get interesting.
Most of the literature that says "MyISAM is better/faster/whatever then InnoDB" is old literature. InnoDB performance has been improved to the point where it is hard to come up with a benchmark that says MyISAM is faster. And there are many other reasons for picking InnoDB.
And, of course, the only useful benchmark for you is to run your application both ways. So, this is a non-answer for your non-question.
Bottom line: Use InnoDB. Period, full stop.