I spent the time to reinstall 4.1.2 yesterday, and it went reasonably well. I would be willing to go back to 5.0, but need to address the issues relating to intermittent availability.
I am running a DSL line with a static IP address (209.147.79.120). The server is operating fine as a 4.1.2 server, and I have no connectivity problems, which would tend to eliminate the issues relating to a configuration issue. The issue WAS relating to access (expecially webmail), where the connection would cease to remain connected. Periodically, I'd get a "web server not found" or "page could not be displayed" message, then get it back in 10 or 15 minutes.
The two network cards are on the approved hardware list, with one from 3Com and the other from SMC. This helps to the better identify both internally and externally.
My URL is
http://www.ournetfamily.com. You can visit the site to check out that I've installed (good, bad, and indifferent). So far today, I've had no connectivity problems.