You can get a stable configuration with both other approaches.
- We run a large site behind nginx with up 5mio page views per day, all requests via HTTPS, backend currently via HTTP (change to HTTPS on the backend is on the agenda). When running behind a proxy, also the backend requires some changes. There are as well more changes involved for secure cookie handling for secure cases, in case you need this. There is a small wiki page [1] for current OpenACS (which is certainly not applicable for your methusalem), which might point to some problem areas.
- with NaviServer+nsssl, the reverse proxy issues won't arise, but you have to handle the porting steps mentioned above in advance. E.g. OpenACS.org runs with current OpenACS+NaviServer. This is a low traffic site, between 100k and 300k requests per day (the same nsd handles openacs.org, dotlrn.org and soon fisheye.openacs.org).
Both approaches run very stable, we every experiences the issues you are mentioning.
all the best
-gn
[1] https://openacs.org/xowiki/running_behind_a_proxy