Chriswahl, thanks for the comment and url, I like it a lot actually and will use it for purely the SAN side of things. In my case with our little SAN (it's got 12 x 300GB 10k disks) I tested raid 5 and raid 10, and went for raid 5 because it was similar for reads, not much slower for writes and I wanted the extra space, and I've no experience with raid 6. Hopefully I won't regret that. I tested raid 5 across 3 disks then 10 disks (the max we can have assuming 2 disks for spare), and 10 disks was very roughly a third faster so I'm thinking we'll go with that.
Re the iscsi networking, we have seen that some changes to the defaults have made significant improvements, although I accept your point and this guy's point What's the point of setting IOPS=1? that the improvement may only apply to a single test VM and in a real world with a bigger load the defaults may be fine. We'll finish testing tomorrow so I'll put what we went for then.