It depends...
I dont quite now how a flat file system works, but i guess it produces much more overhad than any database driven BB which might first of all add to the overall performance and secondly to the bandwith... but especially the performance is influenced by this. Just look at the statistics how many files this forum must have. I can imagine this slows every system down...
Back to the topic of a new bb... why the hell should we keep the old forum 'alive' and not as 'read only archive' anyway? From looking at it 75% of the posts are outdated anyway, so how about a nice new board, a mediawiki (at best connected directly with the board!) and then start all over again. Make stities for the most important stuff/questions and keep the old one as archive?