sylvandb/ArduinoISP — comment on commit a5d34dfde4675dd82792da6efc2f8dbcd2ac81a6
File:  line 0
By sylvandb:

A standard analogWrite() will not work very well because the library PWM is very slow -- the frequency is too low to be reliable as a recovery clock for programming. It might be usable if the fuses had been programmed for a very slow clock (like the ATtiny I had to program which necessitated the bitbang approach) but probably the typical Arduino user will need a faster clock.

I am almost certain that neither 5 or 6 will work. Those are controlled by the same timer as the library millis() and delay() function and so cannot be reprogrammed for a suitable clock speed without messing up the standard library. The duty cycle is also affected, but may still be within tolerance if speed wasn't an issue.

I'll investigate using pin 3.