You can build a 'Release' version by chosing the "Solution Configurations" dropdown list you alreay mentioned. Whatever option is selected here is used when you "Publish the Website".
As for the JITer, it's a fact of life in .NET, and it usually doesn't slow things down such that it's noticable. I mentioned just to let you know that there are lots of other things going on.
One last point to consider -- this is still beta software. They are still working on features and bugs. Performance tuning doesn't come until later.
It's interesting that the startup time of a the website has been such a huge topic for debate. That initial lag has never been a issue for any sites I've worked on. How often do you drop in a whole new build of your website? Really how much of a problem is that first lag time? I don't ask to be antagonistic, so I really am curious if this lag is just unacceptable for your application's requirements.
-Brock
DevelopMentorhttp://staff.develop.com/ballen