I have experience with StorageTek 9310 Nearline silos (with ACSLS), L700 and L180, all configured with 9840 and 9940 drives. All are exceptional, but VERY expensive.
More recently, I have worked with a Spectralogic 10k (bullfrog) with 4 AIT-3 drives, and have been VERY pleased with it's capabilities, reliability and performance.
My ONLY complaint(s) with the Spectralogic 10k are;
1). It does not have enough slots for my backup and duplication requirements. I am constantly swapping tapes out to free up slots.
2). The single slot access door is basically useless if you have to swap out several tapes daily. It's just to labor intensive.
I am in the process of writing up a business case to upgrade to the Spectralogic 20k library with 8 AIT-4 drives. It's features, capabilities and reviews appear impressive.
I believe that the Spectralogic 20k would be the perfect candidate to fit into our existing SAN and future NAS environments...
My 2 cents worth.