Don't do it by ear, it'll have a 'range' of initial timing (lets say hypothetically from 4-8 degrees) where it will all run very similar, and the problem is then it will have the wrong amount of timing higher in the rpm range, that sort of thing.

I'll put it another way - find a guy who sets timing by ear, then get him to set it for you. then check with a timing light and record the actual timing he dialled in. Then drive the car around the block, and alter the timing, and drive it back to him, and ask him to set it again by ear. Then check it. what do you think the odds are that it will be a couple of degrees different this time :)

It's actually quite amazing what float level settings can achieve, About the most significant I've seen (and in this case I'm talking about a situation where it ran 'good' in the first place, not where it was stalling or something) - on a hk holden with 186 and a holley 500, well it would idle and drive fine, but like all motors, it would not like to be in 4th gear (manual box) at below around 15-20mph. (which corresponded to about 800rpm) it'd be fine at light throttle, but try and give it full throttle at those low rpm, and it'd be shaky (and for the record it wasn't an acc pump issue). I took it to a local area with flat roads, and started deliberately too high, then adjusted lower about 0.5mm at a time, and eventually got it to handle 5mph at full throttle in 4th. It didn't go 'great' or fast till it got a few more rpm on board- but it was smooth as silk.

Ironically, the idle rpm/quality wasn't noticeably different by ear from start to finish.