I will share what I know from users across about a dozen customer accounts:

3590 Magstar drives are the Cadillac/Mercedes of the tape subsystems;
though you did not ask about this, I felt compelled to include it!

LTO technology is based on IBM's Magstar, but shared in collaboration with
HP & Seagate;  most customers have migrated up from DLT, so are
(essentially) ecstatic about the speed and reliability of IBM's LTO!  (note,
IBM's LTO is what is considered to be the "Cadillac" of the LTO vendors,
although I've heard good things about Dell's and HP's.)  Price:capacity is
attractive - for a reason;  it's intended to compete with DLT (not high-end
tape transports like 3590 or 9840/9940).

9840's are the "old" (ie, outgoing) technology from STK;  I would advise
you to consider 9940A's, and maybe migrate to 9940B's -- that is the
emerging, latest tape technology from STK -- while the jury is still out,
initial experiences have been mostly positive (using SN6000 as a SAN-based
conduit to a shared library, looks pretty nice, clean... so far).  STK is
highly motivated to make this work!

Hope this helps!

Don France
Technical Architect -- Tivoli Certified Consultant
Tivoli Storage Manager, WinNT/2K, AIX/Unix, OS/390
San Jose, Ca
(408) 257-3037
mailto:don_france AT att DOT net

Professional Association of Contract Employees
(P.A.C.E. -- www.pacepros.com)