The ultimate goal of a TT frame and bars is that you are spending as much time as possible in the extensions, hence why most base bars are a bit narrower to what you would see on a typical road bike (although 40 cm is not super narrow in todays road bike trends).
You will only be on the drops when mounting the bike, some climbing and those times you might need to use them for a bit of stability in certain situations.
I wouldn't swap them out at the moment, build the bike up, spend some time on it and go from there.

40cm is normal.

Agreed. You should really be spending as much time as possible on the aero bars. For me, the only time I'm out on the bullhorns is for braking, tight turns and mashing up a hill. I may pop out for a minute to hydrate or give my back/neck a little bit of a break. But spending any significant amount of time out on the bullhorns of a tri bike is kind of defeating the purpose.

Thanks all...(glad to see your here also Jen!) I modified a old road bike with aero bars and a better seat bike for my first sprint. Honestly, it moves so well that I really had no reason to step into a dedicated tri bike. But I like building bikes, it's a hobby. In my training and the sprint I spent 95% of my time on the aero extensions. I guess what I was aiming at is whether aero drop bards will cost me some watts, compared to the tri bull base bars. Regardless of what I go with, I'll be spending the vast amount of time on the aeros. So in the end, does it really matter to a guy like me? Thanks again!

Ya, if you're building up a bike, make it comfortable for you. If you want 44cm bars instead of 40, then get them. As for power/aero, it's really not going to cost you any significant power. You already know you're not spending a lot of time out there so make the time you do spend fit your needs.

Yes, drop bars will cost watts and you won't use the drops, too far down if you have the aerobars set up appropriately.
The penalty of 40mm extra wing shape on the bull bars is really minimal. Don't worry about that at all. Go with what you find most comfortable.

Several companies make 42cm basebars (I'm in the opposite situation you are; I want a 40 and not a 42).

Examples:
https://www.feltbicycleshop.com/...-3-aluminum-v2-42cm/
https://profile-design.com/...riant=39618238971967

Profile had an Aluminum bar that goes to 46:
https://profile-design.com/...riant=13768834220095


You can use a drop bar, but it's a lot of extra drag (and loss of in-aero shifting unless you are going electronic) for a position you won't use that much. Standard logic is to set up the basebar similar to the hoods position on a road bike (not the drops). You are only using it in situations where aero doesn't matter that much: braking, sharp cornering, steep descents, steep climbs; and comfort/control does

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