Raid 1 will not give double read speeds. (1 drive will be hidden at all times and is a real time duplicate of the first drive)
performance will be a little slower than 1 single drive but provide redundancy.
I have just setup a Hyper-V envioroemnt here at work on an iSCSI attached SAN.
i picked RAID 6 (same as raid 5 but with 2 parity drives instead of 1)
its provided quite nice performance while still giving me the redundancy we need.
how many drives are you looking at using?
we currently have 8 drives (450gb SAS 15kRPM) with expandability to 12