I wanted to install the latest snapshot, so I went to
http://ftp.nluug.nl/pub/OpenBSD/snapshots/amd64 and dd'ed install56.fs to usb. However, it gives an "ERR M" — probably my BIOS cannot handle it. The usb stick boots fine in my newer computers. I also have problems booting cd's on which I burned install56.iso (even though they, again, boot fine in my other computers).
Is it fine to boot from the official installation medium (5.6 release), do a clean install and select the software sets from http, pointing to the snapshot (same url as above)? Or should I expect the installation software (5.6 release) to be incompatible with newer software sets (snapshot 2014-12-27)?