RE: Performance of 2780 controller and 141GB drives

You've got several factors going:

1. Mirroring is faster at writes than RAID5.  Reads in general won't be
faster but probably won't be slower by a measureable difference. 
2. Service times on 15K drives are noticeably better than on 10K drives.
3. Ultra320 SCSI drives vs. what, 80MB?
4. PCI-X bus vs. SPD.  This is a huge difference.
5. 1GB Read, 3.4GB Write cache on the new controllers.  If your old
controllers had cache, it was no more than 26MB.
6. Faster chassis interconnects for the new box (I'm assuming it'll use
the 2GB optical).
7. Your new box probably has more RAM and certainly has faster
processors.

I think you'll easily see a boost in overall performance.

BTW, I'll be moving our DR box from 62 10K 17GB drives to 42 of the 15K
141GB units in the next few months when it moves up from an 8309 to a
570.