I was looking at my wife's position who uses that as her primary road bike position (she has pads - she is not racing any longer) and pictures of my son's on the IAB and the biceps are about your angle. I certainly understand the argument for a longer stem stretching you out.
A longer stem and allows putting elbows closer, more aero tends to roll the shoulders more. I see few riders get their elbows that close in IAB, so it should not be an expectation, but it is more aero.
Unfortunately in Grand Junction Ref Randy mentioned IAB was not the best thing. So when the camera was near - you didn't see it.
This setup was good enough to be fastest of the day for Collegiate Nationals. As you know - by a whole lot.
Attachment 564561

This is IAB TT training angle from the back. The issue here was the head was too high and we worked on the turtle tuck and improved a bit. That was good for 28min @ 28mph (17-18 1st/70) a few days later, 300ft climb in 7 miles and back.

The year before you can see 1-2 sec of IAB position. He started with elbows close, finished with them wider, but also going 30+mph in junior gear so there was a stability factor.

This is a RR setup. Bars are 1cm or so lower, as is seat. IAB still works.
https://vimeo.com/126378398

It doesn't look like your kid flares his elbows though. It's the IAB position + the flared elbows in the other one that makes me think a longer stem may make sense.

I think you may be right, just that my kid is faster on the shorter setup with seat way forward.
The new built-for-IAB bike is 2cm shorter cockpit. He kicked seat up and forward and is more over bars and the stem is shorter. He has not used it for an ITT (sadly for the builder) but he is way faster on it, mostly due to aero stuff I expect.

ToC/World Tour IAB
I am trying to verify this was in the TT. Seems so. Disc and disc brakes. Very weird setup. Product placement for sure.
Attachment 564694

Bought a new stem today (120mm, so 1cm longer) and pushed the seat up higher. Conveiently I cracked a new sprint best 5s power today. Nothing to do with it, but still. Saddle was probably a bit low looking at pictures again.

As far as the IAB position is concerned, when I did it (very briefly) during my ride today, I felt I could bring my elbows closer together and still remain stable. I'll try and a get a picture, but might be low on luck for that.

That makes me feel not so bad about rounding my back lol.

related to bike fit - i lowered my saddle earlier this year but think i need to go even further. stage race this weekend so don't want to mess with anything now but might try early next week.

on another note, is it just me or do shimano 11s chains shift noticeably better than KMC?

I do prefer Shimano chains to KMC. The shifting difference is not huge, but there is a difference.

Never tried KMC chains, always used shimano chains and cassettes ... even with sram drivetrain.

The new PTFE coated chains handle angle better and shift better than the prior 9000 that were great already.
I moved from KMC with 9000. I can't speak to anything newer than the last 4 years, but I'd be surprised if anything shifts and rides better stock.

this was ultegra level, not 9000, but glad to hear i'm not just crazy.

Rode in club fit jersey with disc gravel bike and road wheels a few days ago. My friend was in speed suit, aero helmet, deep wheels, aero frame. It was pretty windy too. I noticed that on downhill cross winds, he would coast down the hill faster in the hoods and still accelerate faster than me, in the drops, spinning out at 50/11. He's a bigger guy than me too. It must have been the wheels getting the sailing effect. Crazy to see the difference in real life. Aero is everything

Wouldn't that muddy the waters and make it likely that he'd descend faster? Bigger people tend to have more weight per aero profile.

Also, it's hard to compare without more specifics on things like "in the hoods." How aggressive does he have the hoods? How much bend at the elbows?

Does anyone use deep drop and/or long reach bars, or is everyone on compacts? Getting a new frame soon and I am considering the Aerotundo, which has a longer reach and deeper drop than most. My Trek currently has compact bars. They are fine, but I think I like the classic bars on my steel bike better. The different positions seem, well, more different. One thing I worry about is that the new frame has a shorter headtube, so if I set the bars lower, maybe I'll find the drops too low. I don't know. What do you think?

You can always use an upturned stem to get your drops where you need them.

I doubt that would be necessary, a spacer or two at most. The difference is like 3cm and I would prefer if the bars on my current bike were a bit lower.

I am running Aeronovas on my new bike and I really like them, EXCEPT that when you sprint from the drops going uphill you are going to bang your wrists on the bar. Besides that they are supreme.

Do you like the extra reach? I guess it is just compensated with a shorter stem, so maybe it doesn't matter. Mostly I am wondering whether the extra drop of the Aerotundo is worth it or whether I'd be better of with the shallower drop of the Aeronova or a similar bar (Aerofly, EC70, etc.)

I think I mostly appreciate the shape of the bar and the various hand holds it has. On my Tarmac I ran a 140 -17, on my AR I have a 120 -6, reach feels no different as far as I can tell.

So uh, I guess my answer is kind of a shrug? A shallow bar may be better for sprinting, but I might just have awful sprint form. Considering all the stem options available I think it basically comes down to how comfortable you find the shape of the bar.

You're probably right. Hard to know without trying unfortunately. I do like the idea of having several hand positions.

Main reason for me to use crit bend bars for 30 years. Black and blue forearms after hard sprints.

The FSA compacts I use have the same effect as crit bend bars, no forearm contact. But need a longer/lower stem to make up for lack of reach/drop.

The aerotundo's seem to run a bit wide, and I didn't really like the shape.

I was on protundos but have switched to Zipp aero bars - love 'em! No wrist-hitting issues with them either.

They aren't super deep, but not compact either. Definitely shallower (and shorter) than the protundos

edit: "protundo" = "pro rotundo"

I was going to suggest you look at the Zipp Aero bar if you are banging your wrists on the bar. It sweeps forward and the drops flare out giving lots of clearance in a sprint.

The Easton EC70 Aero does not have as much clearance, though the drops do flare out.

As a side note, on these bars with the flared drops, a 40 will measure 42 at the drops.

I use the aeronovas. Absolutely love them. Used compact before and don't ever plan on going back.

It's not just drops, but my hoods are much further away, too. I like it a lot.