GlowBoy

One thing I didn't mention in the OP was that I mostly don't end up riding in darkness on my morning commute, and I'm looking for conspicuity in (overcast) daylight . I don't always run the high beam in the morning, so regardless of how you feel about the "wash-out" issue I think the quest for a bright blinky is still a valid one.

Exactly! It is a never ending quest. 800 lumens out of the high beam (Philips 35W x 24deg at 12V) is nice, but on rainy nights I could definitely use more. Can't wait for the 14.4V upgrade to 1440 lumens. Meanwhile, back to the original question and what seems to be nearly a consensus answer:

Fair enough. After such a strong response I was even starting to doubt myself on this one.

So no better way to find out than to actually try it. This morning I parked the bike with the 800lum high beam on, and the wimpy little EL410 on in blink mode. High beam aimed down a bit towards the pavement, blinky aimed straight ahead, both as they would be in normal use. Checked it out from 100' away, a block away and two blocks away. What do you think I saw, guys?!

Well, you are all partly right, in the sense that the blinky is not clearly distinguishable as a separate light at anything over 50-100' away. However, it still adds a lot to my conspicuity profile, even at a distance. It makes the high beam very noticeably and visibly appear to pulse -- even at a quick glance, and even out of the peripheral visioin. It's attention getting, and distinguishes my vehicle clearly and quickly as a bicycle that may not be moving at the same speed or in the same pattern as other traffic. This is exactly what I'm hoping to achieve, and a brighter blinky would help me achieve it even better, as I originally suspected.

I pick bike! People are very respectful towards bicyclists around here. [And yes, I realize this is not true in "normal" America. Every day of my life I count my blessings that I don't live there, believe you me.]

And thanks for acknowledging the obvious: that a blinky will help distinguish me from the other traffic.

The key is to have people realize you're there, even in complex traffic situations where you may not always be visible because of the other cars in between. People may not always have clear lines of sight to me, and I want potential conflict partners to notice me even if I'm not in their field of vision constantly. Think of one of the most common bike-car conflicts: I want oncoming traffic that might be turning left to notice well in advance that there is a bicycle on the right side of the road, even if they only see me intermittently in between the cars that are passing me, and not to make a sudden left turn -- directly into me -- right after they think it's "clear".

For me, when riding in traffic conspicuity is not an issue of whether people can see me -- any idiot legally able to drive can see a bike with a simple blinky and no headlight. It's about being noticed further in advance. It's about being noticed amongst all the other enormous amounts of light pollution -- much of it constantly moving and changing -- on the road. And I'm still (more so than ever) convinced that a reasonably bright blinky (30-100lum) can help achieve that, even in addition to a very bright steady light. Thanks for the discussion, and for prompting me to prove things out.