Another embedded x86 platform is PC Engines's ALIX, it's moderately faster than the Soekris offerings.
http://www.pcengines.ch/alix.htm
As for the system you mentioned in your first post, ARM platform aren't really standardized.. so running OpenBSD on that specific system would require that you port it (..and possibly write additional drivers).
There are a few embedded ARM platforms that are supported, you can find them
here.