That sounds about right. And yes, it's obviously an OB issue - this whole discussion started out by Igor wondering why people don't like using OB. I think a major part of the answer is just that.
It is definitely not an issue of OB, but an issue of the extensions that people load with OB.
If you try the Seaside One Click image you will notice that OB is only marginally slower than the old browser.
Lukas