Am I correct in the reading that you have ONE host server? Enterprise plus is a lot of licensing costs for features you can't use with one server.
RAID 5 vs RAID10 is always a trade off involving "good performance" vs "slightly better performance", and "losing some space" vs "losing a lot of space".
You've mentioned repeatedly that there's almost no load, so I don't see why you would use anything but RAID5.
Finally, iSCSI reservations are much less of an issue in ESXi 5.1.
PS You do have the FBWC on that RAID controller right? That's going to have more impact than your RAID level.