I got my Steam Machine on Thursday and after running initial updates, I tore it apart and installed my Crucial RAM and 2TB SSD. So far it's running great, 32GB and no apparent memory instability issues. On the fresh SSD I installed SteamOS, then repartitioned it to shrink SteamOS to 1TB and made two 512GB partitions, then installed Arch and Windows on them. Triple boot with rEFInd is working well.