Possible disk IO issue

I've been doing a bit of research in this area lately myself. There's a great calculator here that people on this site have pointed me at. Throwing some basic numbers into it with a 97:3 read to write ratio and not factoring in cache hits, it looks like your array should be able to mechanically deliver about 675 IOPS at 4k. You're doing 902 transfers per second which would be high, as your queue length per disk also indicates.

You might also measure sec/Transfer and %Disk time. I've found %Disk time to be rather odd with RAID arrays, and I've found it more accurate to measure %Idle time and then use the formula 100 - %Idle to calculate busy time. I bet you'll find that your disk is very busy and you'll see a lot of 20ms+ transfer times. IMO these numbers are more clear cut if you want to conclude that you've got a disk problem.

Here's a great article that gets referenced quite a bit. It's dated but relevant, and is especially useful for explaining why %Disk time and Avg. Queue Length can be difficult to interpret.