Performance Monitoring of Mirrored SCSi

I have a server with two 16 Gig 7200 SCSI Hard drives. They are connected to an older SCSI card. Can I use performance monitor to find out if
A:The SCSI card should be replaced with a faster one and if so how much impact would this have (40 MB/s-> 80 or 160)
B: If NT mirroring isk killing the performance and by how much.

Is there another utility that I should be using instead