To ease the estimation, how much the deactivation of ns_cache might cost for a particular OpenACS instance, i've added a summary line to nsstats (in the "Cache" statistics page, committed on bitbucket). E.g. on OpenACS the updated statistics say currently:
ns_cache operations saved since the start of the server 18m 39s on 286.69K requests (3.9ms per request on average)
3.9 ms is the average value on requests, including static pages, for which the impact is most likely lower than on content pages with caching from DB requests. Some particular caches, which are not used on every request, might yield on a hit much larger savings, so there will be some spread.
