Will this hardware combination work well?

Can I assume that you have virtual machines running on the netapp? If so, you need something vm aware or your backups probably won't boot. Have you looked at the netapp options? Their replication and backups to another netapp are a big selling feature

> should I try to upgrade the LTO4 drive in the Tandberg to an LTO5.. and if so would the speed difference be enough to justify it?

No way to tell.  What's your current bottleneck, and what's the maximum you can read from the source when doing a backup?   You could put a tape drive capable of backing up 1TB/second, but if your disk can only feed the tape drive at 40MB/sec, that's all you're going to get from the tape drive.  

There's not that much difference in speed between LTO-4 and LTO-5 -- native speed takes a step up from 120MB/sec to 140MB/sec.  So by replacing your current drive you gain 20MB/sec times your compression (if the NetApp can feed it enough data).  By adding a new LTO-5 and keeping the LTO-4 in service, you'll at least double your effective performance.  In any case, the LTO-5 almost doubles the capacity of LTO-4.  With 1.3:1 or better compression, you'll likely be able to fit a full backup on a single LTO-5 tape, making your backups, restores, and archiving easier.

I think you've got a reasonable plan in buying an LTO-5 drive -- just be aware that you typically can't later use the standalone LTO-5 to upgrade your autoloader (due to incompatible firmware).  However, by the time you need to worry about that, you may prefer (if possible) to upgrade the autoloader to LTO-6 or LTO-7.

Consider also that you might want to make two copies of your full backup -- one to keep onsite for a quick restore if needed, and one offsite to protect from a site disaster.

thanks guys.  I'm also looking into the possibility of upgrading the drive unit in the Tandberg to an LTO-5.  I have a BU job currently that nabs about 60% of the Netapps used space deemed important enough.. the job typically takes 13 hours and processes at an average 2250MB/min.  If I add another say 40% then I'm looking at around a 5 hour increase give or take.

Right now I only have one BU job that targets netapp data, Saturday nights, full backup, compression hardware (if software then none), Encryption (Hardware, if not then Software).  NDMP options include backing up ACLs and file history.

Inspecting this last job log, out of the four backup Details, the rates were: 1707, 2339, 1802, and 2931MB/min.  the slower parts were because that vol is housed on a SATA shelf.  All are FC uplinks, the Netapp is using 1 GB interface uplinking to the backup switch, and the tandberg loader is an external SAS to the BU server.

The data you've posted just confirms what I said in my previous post.
1) Use HW encryption on the tape drive if encryption is required.  Using SW encryption may drastically reduce your performance.
2) If your backup jobs are performing under the minimum rated speed of the tape drive (for LTO, that is as low as 1/3 of the native speed for HP drives, somewhat higher than that for other drive manufacturers), you will prolong the life of your tape drive and media by disabling any kind of compression (when a tape drive is compressing data, it empties the buffer sooner, and if the storage and rest of the path to the tape drive is not up to the task, you'll get more buffer underrun and more wear on tape and the drive mechanism).  Note: disabling compression may or may not mean that you will need more tapes to store a complete backup... it depends on how compressible your data is now, and how full the "last tape" is now.
3) Since you're not (with the possible exception of the one 2931/min job) feeding the tape drive enough data to keep it streaming, you won't see any performance benefit from a faster tape drive.  The tape drive is not the bottleneck.

In my previous post, I gave you two good options; it's up to you to weigh the cost and benefits of the options.  Again: a faster tape drive will not give you faster backups; the tape drive is not the bottleneck.  The options are
1) Buy a second (LTO-4 is good enough for performance and the tape and tape drive may last longer due to less buffer underrun, but you'll miss out on LTO-5's almost doubled capacity) tape drive, and perform your full backup sending half the data to one drive, half to the other.  If you do decide to buy an LTO-5 drive, use it for your fastest jobs, and turn off SW encryption (HW is OK) and any compression.
2) Don't buy any new HW.  Realize that you can divide your data into two logical sets, call them 'A' and 'B', and do a full backup of set A on Friday, and a full backup of set B on Saturday.  On days when a set is not getting a full backup, perform a differential (i.e., Saturday - Thursday for set A, Sunday - Friday for set B).

or you could go to "Incrementals forever" + Synthetic Fulls which would reduce the sizes of your backup.

Thanks SG.. I often forget or otherwise don't think to break down the numbers, much to my detriment. I bought the sata shelf for large amounts of storage but never once thought it'd be slower if I had to back the data up.

Your advice here also lead me to rediscover an aging file server in another site that's the single large contributor to latency in that admins Full job.  It will be replaced when their SAN goes in but in either csae thanks for your help on this.