i would recommend a pci-e sata2 host adapter and external sata2 striped drive array. if you have your disk array on the same internal sata bus as the main drive, you'll still likely get a bottle neck with disk cache enabled in ae.
barefeats.com has several reveiws/benchmarks of various sata2 cards and raid configs, as does
amug.com. although sas is very fast, i would lean towards sata2 over sas for the disk array just based on price per gb. but you could look at an sas drive as the main drive, the small read/write times are great on sas drives which make them a good choice for boot drives and disk cache drives. the newer western digital velociraptor (sata2) has also good benchmarks and will now easily install in a mac pro internal drive bay.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW
