the most simple and efficient test is to count the number of external files (css & js) loaded on each page.. this tells enough about the speed..

Example:
Dolphin 6.1.x
Front page - CSS + JS total file size: 174 kb
Front page - External files loaded: 3 css files and 10 javascript files
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Dolphin 7 alpha 12:
Front page - CSS + JS total file size: 632 kb
Front page - External files loaded: 17 css files and 30 javascript files.
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Dolphin 7 alpha 14:
Front page - CSS + JS total see more file size: 882 kb
Front page - External files loaded: 12 css files and 12 javascript files.

This is a big improvement from the alpha 12.. in my opinion D7 is far more complex than D6 on features.. so it can't be lighter..

btw I recently read on a blog that in IE 6, 7 and even 8 limits the css import to max 32 files and 288 kb each - everything above these limits are not parsed, so beta 14 is a big improvement..