WeBWorK is pretty RAM intensive and each active "RequestWorker" can take up to 800meg of RAM. If there are too many active workers swapping occurs even if some of the workers are idle. It's actually much faster if there are fewer workers -- if too many requests come in at once the response might be delayed a second or so but that is less disruptive then if the server is constantly swapping memory. A value as low as 10 workers or even 5 might work faster for homework. (The situation for gateway quizzes when everyone submits at the same time is different -- in that case get more RAM :-) )
--Mike