The gap between Linux and Windows being different in performance was closed when PHP 5.3 was released. There were many fixes to improve performance on the Microsoft platform. Microsoft also released Wincache which speeds up PHP on Windows significantly.
As for that link, many points are Wordpress specific, and it's almost near trolling so I wouldn't read too much into it.
SilverStripe works well on Windows Server 2008+, IIS 7.x and SQL Server 2008 or MySQL on Windows.
Performance is not really an issue at all, and all features work out of the box. We also have continuous integration builds running on Windows, so any issues are caught if they're unit tested, thus most of the core framework and CMS work fine.
The only time it won't work is if your host is providing IIS 6, which does not support rewriting and is more of a pain to get working. If this is the case, you'd be best to go with a Linux host.
Otherwise, my recommendation is go with what you're most comfortable using. If you've had a lot of experience on Windows, then use that. If you're a command line jockey on Linux, then go with that instead. Ubuntu and Debian Linux are very good operating systems, and SilverStripe works very well on them.
There are a few downsides to using SilverStripe on Windows, but they mostly can be worked around relatively easily unless you're working with command line tools that require a *nix based platform.