Thought I'd chime in here and add myself to the list of successful installs and say thanks!
ESXi 5.1 with 5 VM's (my test server)
i920 w/P6T SE MB
18GB RAM
120GB SSD
1x250GB HD
1x500GB HD
1x1TB HD
3 drives mapped to RDM and SHR in xpenology (1CPUx2Cores, 2GB RAM dedicated)
Transferring about 80-100MB/s with 5% cpu usage. I've been testing Plex on it as well. Using Plex to an Android device I see about 75-80% CPU usage. Overall very happy with the setup. Looking at going to 3TB drives soon to take some of the load off my poor DS411j.
Anyone play with iscsi throughput on the xpenology/esxi builds?