Without optimization EPiServer can be quite slow at cold start, but serves pages extremely fast unless you run out of memory in the app pool - and you shouldn't with 8 GB of RAM.
Things to check:
- App pool behavior: does CPU spike with every page load? Is the app pool using a lot of physical memory? Are there any memory limits imposed on the app pool?
- On the start page of Admin mode of the site backend there are cache stats. Cache hits should be really high (> 90%) or something is wrong with the cache.
- Are you sure it's server-side lag - what does Developer Tools/Firebug say?
- Have you enabled log4net logging? It can be extremely useful when troubleshooting performance issues. If yes, have you mapped your own configuration file? (we had extreme performance issues from that - use the built-in mapping to episerverlog.config)
- Are you having issues with all templates? What if you create a barebone test template with no master page/main layout view and do nothing but output a property.
- Any suspicious events logged in the event log?