Reading this quote below from the first page of this link http://arstechnica.com/business/2011/11 ... for-nginx/
suggests that maybe Apache is the way to go since my website is highly dynamic (95% of none help pages go after the database with a few functions doing multi-pass work).
Nginx particularly excels at serving static files—like the Tectonicus map tile images. For larger websites, it's often employed as a front-end Web server to quickly dish up unchanging page content, while passing on requests for dynamic stuff to more complex Apache Web servers running elsewhere. However, I was interested in it purely as a fast single Web server.
At the same time this extract from the same link above suggests that maybe I should try to get "Apache MPM worker" installed but will PHP handle it as I add more to the quote and underline the concern?
The drawback to doing everything with processes is that Apache prefork can be a bit of a memory hog, especially under load. Another precompiled flavor of Apache can be installed as an alternative: Apache MPM worker. "Worker" differs from "prefork" in that worker's processes are multithreaded, giving them the ability to service more requests with fewer system resources. This can translate into faster pages served with less RAM and CPU. However, because some Apache modules don't necessarily work well when run under multithreaded Apache, you have to specifically select this version to install on Ubuntu and on other GNU/Linux distros with package management.
A bit of searching showed that Apache worker could go a long way toward making Tectonicus serve its tons of tiles faster, but switching would cause some issues with PHP. The built-in Apache PHP module, "mod_php," is one of those modules that can have issues running multi-threaded. I was faced with quite a bit of software ripping and replacing to switch from mod_php to a standalone PHP.
Still reading! It looks like they have worked around the PHP issues - maybe ????. Like you suggested Celauran. Trying both may be wise.
So the reading is done. It sounds like Apache is the way to start with a consideration of using Nginx as a way to maybe speed things up later.