This is a long time coming for you, but this is why I am jumping from Wordpress to SilverStripe. I started with one blog in 2007, now I have 128 domains, and 61 blogs I update daily. I love the fact that I can gain more advertising real estate with multiplication of effort. However, WPMU really tore my heart out. It promised everything and did nothing for me in the end. Wordpress blog I love, but I grew tired of upgrading everytime I turned around and honestly, I am looking for a Content Management System now, which wordpress is not. You see, I still want all that ad real estate, but I don't want the workload!
Now, with Silverstripe, I have gained one admin area where I can easily house my entire online empire. It will actually appear as if I have more than 61 online efforts because with SilverStripe I now have really nice looking web pages plus I gain the forum that integrates seamlessly and I was easily able to drop my chat in the site. It never really looked right in Wordpress, too small for the side bar and too hard to find as a page.
SilverStripe has one draw back though. The Blog Module reminds me of when I started with Wordpress in 2007. It is very basic, but functional. Honestly, it is really slick and a back to basics mentality is often better than all the bells and whistles I cluttered up my wordpress blogs with. So it was a trade off, but SilverStripe is not that hard to pick up. It is mostly PHP and the people that put this together are really brilliant in concept.
SilverStripe for me, was a God send. Sure, it is a whole new animal to tame, but I think that Silver Stripe will grow with my online effort, where wordpress, seemed to plateau despite all the great widgets and bells and whistles for my own personal and professional needs.
I am a newbie to SilverStripe, but in a little bit of time, my site is almost ready to launch. It was not complicated as my demands for the vision that wordpress just could not accomplish for me.
I really hope that helps, even if the answer is late in coming. I just ran across your post looking for a way to integrate my wp blog archive with silverstripe itself. A simple redirect will work just fine!