Quick clarification... "The average disk queue length is quite well documented in that it should not exceed 2 per CPU" should be "The average disk queue length is quite well documented in that it should not exceed 2 per spindle", but that common knowledge is not neccessarily true.
More information on this topic from the Microsoft SQL support team here: http://blogs.msdn.com/psssql/archive/2007/02/21/sql-server-urban-legends-discussed.aspx
As I read your question, you want to know how many IOPS (IO's per second) is high for a hard drive. The answer is "when you have more than the drive supports". a 15K Seagate Cheetah supports many more IOPS than a 5400 RPM laptop drive. In your case, you have the drives setup as RAID 1 (which adds redundancy, but reduces the available IOPS as you write the same data twice).
Courtesy of Wikipedia (http://en.wikipedia.org/wiki/IOPS), some standard numbers:
- 7200RPM SATA drives - ~90 IOPS
- 10kRPM Serial Attached SCSI drives - ~ 140 IOPS
- 15kRPM Serial Attached SCSI drives - ~180 IOPS
- Simple SLC SSD - ~400 IOPS
- Intel X-25 M (MLC; As of March 2009[update], no competition) - ~1,500 IOPS
- Intel X-25 E (SLC; As of March 2009[update], no competition) - ~5,000 IOPS (Intel's data sheet says 3,300 write, 35,000 read IOPS, while 5,000 are measured for a mix)
- ioDrive, a PCI-Express card with Flash - >80,000 IOPS
- DDRdrive X1, a May 2009 PCI Express based solid-state drive - 300,000+ (512B Random Read IOPS) and 200,000+ (512B Random Write IOPS)
- Violin Memory Appliance, 1,000,000+ Random Read IOPS