XSAN vs Storage Server 2008 R2

I am looking for a viable option for shared storage between a server either running XSAN or Storage Server 2008 R2. Of course, one is apple and the other is Microsoft. Though this is my question, we have two departments that use strictly MACs and other classrooms that have all MACs that dual boot into Windows 7. I would like to use our current EMC VNX 5300 to connect via ISCSI...no FC support.

For strickly apple sharing/storage would it be better to go with OSX Lion Server running XSAN 2.3 to "natively" support AFP? I have tested the ExtremeZ IP product and it works great on the Windows side to OSX clients to connect, but it is pretty expensive compared to getting Apple Software at an educational discount.

My other question is if anyone has used the Promise SANs at all and have had good/bad reviews? I would like to keep the departments and classrooms that are strictly MAC OS on their own shared storage instead of going through our current SAN (VNX 5300). Also I am new to the XSAN software but am proficient with SAN software/management. Can XSAN be integrated into Windows AD to create quotas like within Server FRSM?

Thanks in advance