How I'd do things 😊:
I would like to see the login box as a box, instead of part of the header. This way the header would not have to change and I never fancied typing in my login information on the top right. Furthermore we could use this position for banner ideas. This way the status information found in Carls design could be preserved.
Take the new dog. It looks more like Alex. But don't double the O in OpenACS (if you look at the logo, there is already the O around the dog, so no need to double it within OpenACS again).
Use Carls "Learn more about OpenACS". I really like that one, cool work. It is colorful, jumps into the eye, still slick and dynamic. Though our graphic designer is bashing my head for this comment 😊.
Round edges with a second color as a seperator. If we need this for the header as well, hm....
All in all I think Design #3 resembles more of a graphic design attitude with many elements taken from guidelines established over the years.
How to proceed? There needs to be someone to actually do the work. He can and should take a lot of guideance from this thread. But I'd leave the final decision on the differences in design (between Carl and #3) up to the person who is actually doing the work.