I don't understand why we need to do pro and con's on frames any further.

There clearly are downsides. Non that really justify changing but ... these are just ideas.
And it's op to you. So really no need to argue.

That being said, i'm fairly sure that the "not needing to load the menu" time and time again
is not really relavant. what is it 500 bytes of html? As oposed to opening a new connection every so often
to download it entirely again, or check if that page was updated.

Also in general I doubt tabs have an inpact on performance, nor in the + nor in th -

Well the discussion popped up so we decided to discuss it. Well proven point Inferno.