I'm sure someone will jump in and tell us how much you can do with tWindows Server (...one of the four versions they sell...), but IMHO, there's a whole lot more dvelopment going on in the NAS world than there is for Windows server. There is a good amount of competition in this sector, and it's driving more and more features into the NAS software packages. Windows server has been pretty much moribound in the same time frame. So, today I like the features that QNAP has to offer, and I suspect that in the near future this trend will accelerate.

Those are all good choices. The features that you get as you move up the ladder probably don't matter much to you, except maybe Real Time Remote Replication, since you have somebody whos more or less permantly at a rempte location. This feature is available on all the Intel-based units. The other features you get with the high-end models, are primarily focused on advanced networking schems, such as: VMware Certification, Citrix Certified, Microsoft Hyper-V and Windows 2008 Failover Cluster. It doesn't sound like you need that, yet. The one other thing Intel units have is AES 256-bit Volume-based Encryption, but it's quite slow with the Atom CPU, and it may not be an issue for you, depending on your physical security situation.

Now, the OTHER thing you get as you spend more mony is WRITE speed. Take a look at QNAPs published write speeds:

Write Performance (MB/s) - Dual-Core Atom: 107, Single-Core Atom: 88, Marvell 2.0GHz: 75, Marvell 1.6GHz: 45

This has a direct impact on yur backup speeds, although the laptops may be the limiting factor anyways, if they have the typical 5400 RPM HDDs in them. They use less power, so it's quite common to use them instead of the 7200 RPM models.

The other thing you get for your $$ is USB 3.0. This may not have any impact on your intended usage, but for some, USB 2.0 is a deal-breaker.

Of course, you also know that QNAP released a couple new models at CES, right. I tell you, I can't keep up with them... LOL

Bottom line, like Anna above, I think your expectation for backup performance is the key discriminator here. That's the primary area (of the ones you listed), where spending more will get you more.

Here is a direct comparison between the units you mentioned:

qnap.com/images/products/comparison/Comparison_4BayNAS.html

There's no doubt that the major NAS players are continuing to drive more and more and better features into the NAS side of things. QNAP just release version 3.6 at CES this month, which is two releases beyond what I tested in this review.

That is a VERY NICE surprise!

Usually when the "Manufacturer reserves the right to update the product specifications" it's to take cost out of the product.