If you're mostly serving text you can serve a lot over a 128K aDSL line. Each page will be a few KB. Once you start serving lots of images and graphics you'll start to get clogged up bandwidth.
Regarding your system load, do your wimpy point presentations include graphics and images? If so, streaming them to your users will be somewhat CPU intensive. I would be surprised to see it so high, though, with seven users on a relatively low-bandwidth line.
You've got plenty of memory, so ...
Are you starting the postmaster with a high -B value? (if it is low, you're probably doing a lot of transfering from OS filebufs to the buffer cache, which is cycle-intensive). The PG default of 64 is far too low for any production work.
Have you vacuum analyzed your database after adding significant chunks of content? This is a crucial point in achieving PG performance.
Lastly, knowing that the load number is high isn't of all that much use without knowing which processes are chewing up all those cycles...
