Thank you for your thoughts.
My bike fitter recommended me the 400mm width and I feel comfy with it. I got an older bike which has a 380mm handlebar but I mainly use in on the trainer or when my other bike is in the garage; anyway, the smaller width is OK but I notice that my elbows tend to "latch in" while I stay more relaxed on the wider bar.
I live in a rather flat, wavy at the best, environment but with lots of wind (the sea is not too far away). I usually do longer rides (4-5 hours) and I hardly ever participate in competitions.
I like riding in the drops especially when fighting the wind but I tend to switch often because there is traffic, traffic lights or crossings where I need full control. I guess, in the end, I am riding most of the time on the hoods.
@PLA: Nothing in particular, yet. Read some articles and reviews.
@jonathanf2, I don't have the "knee hitting bars" issue but your thoughts on stability are helpful. Usually, I go low against the wind but stay in the saddle; I don't feel very comfy sprinting or accelerating on the drops.
So, I might stick with my 400 on the hoods and go slightly wider on the drops!?