As I posted before, it's not much more effort to do caching "right." I've done this for the 3.x bboards...
The very simplest way is to have the insert script erase your cache for the portal rather than waiting for the cache to time out in N minutes. This can even improve performance if post frequency is low enough -- openacs.org still measures minutes per post rather than posts per minute, I'd guess.
As I've also asked before -- is 4.x THAT much slower than 3.x? If so, shouldn't this be ringing alarm bells somewhere?
