looking at the basic info give here I would choose the IBM for two reasons:
a: the fact that there are twice the number of iSCSI ports per controller, this would mean more bandwidth to the SAN, this = better perfromance
b: the fact that there is twice the amount of Cache per controller, this would mean more IOPs, due to more data being stored in the faster Cache location, this again = better perfromance.
depending on the capacity you require I would go for the 600GB drives, as the rebuild rate on Disk failure would be quicker, resulting in less degregation of service due to rebuild.
also if you can afford the capacity loss, create the array as RAID 10 this will give the best possible Read/Write performance.