I have had a blog for around 4 years now that has gained some success and gets tons of residual and organic traffic. I am using an outdated version of BlogEngine.NET and we are going to switch to WordPress. Currently, our blog is at ourwebsite.com/blog, and I don't really want to mess with our web server. I setup a new server just for WordPress and instead of dealing with proxies and things that are above my head, the new blog will be at blog.oursite.com. I am trying to figure out the best way to go about doing this. We value our search engine rankings very much so, as that is where 90% of our traffic comes from. Would I be best off:

1. Importing all of the old blog posts from oursite.com/blog to blog.oursite.com and then redirecting all of the articles, categories, authors, pages and tags to the new blog and giving up the direct links to our current site.
2. Keeping all of our current articles as they are, and only add new content to the new blog.oursite.com and just kind of let the old blog float around our site.