After testing with different user's (with pretty low profile machines) we reduced the number of transparencies (rgba & opacity and PNG transparencies) and solved the problem on those machines.
I've coded the BBeditor to use css-sprites to make it "faster". If anyone wants the code, i can share it css & JS.
It also added a nice option for the forum to show avatars on the left or on the right of the post based on users preference (chosen on my account). And was so simple... Fool of me, tend to overlook DF features =/ in the past ;D.
I've learned a lot of DF with this redesign, hope to share that knowledge and lesson learned soon.
They all use a custom content module I've written which does away with blocks and allows a customisable page layout. Content is loaded from various places (including existing DF blocks if required) and put into containers that are then laid out with CSS to whatever design you care to implement.
The base theme was reDesign3 but quite a lot of it has been cut out on these sites.