Best options for Video Editing

The last update to the Mac Pro desktop was in late 2013 when the silver tower was replaced with the black cylinder.

The following gives performance of the various Mac computers as well as external storage units.

http://macperformanceguide.com/index_topics.html

A 2009-2012 silver tower is highlt upgradeable

You can upgrade graphics cards and even use a lot of PC but PC cards do not give you a boot screen

User Tip: Mac Pro silver tower (2006-2012) Replacement Graphics cards

http://forums.macrumors.com/showthread.php?t=1440150

You can install a fast PCle-based blade SSD

SSD Blade Drive for "Classic" Mac Pro

You can install a USB3 PCle card but note that you can't boot from a USB device connected to the USB3 card

Yes, those upgrades will help a lot.

You haven't mentioned what editing software you intend to use.

Russ

A lot of this has to do with your budget, what/how your are editing now (as Russ mentioned, the software) and other variables. Setting up your machine with a couple of upgrades and tweaks could be fine for you. (eSATA card to hook up a couple of external RAIDs if you are currently just editing on an external Firewire drive or single internal drive.)

An SSD drive for booting is really a great upgrade, together with throwing some more RAM in. The graphics could help, depending on the software you are running. Some software may not use the graphics card.

The one caveat is that Thunderbolt (for me) is really a great thing to have when moving a large amount of files. I am often moving 10-15 terrabytes arounds for back-up, additional drives and the rest. You can a fast eSata card and enclosure. But then if you go Thunderbolt later, you may need to move things around. (There are some Thunderbolt to eSATA devices, like those released by Firmtek, which I have used and some enclosures with Thunderbolt and eSATA connectors.)

Not sure how many cores or speed your computer is, but my Tower is older and does pretty well. Faster than my newer iMac (though not the most recent one.)

So in a nutshell, you may be able to get a ton more out of your current computer for less cost. I much prefer my Tower to my iMac, but for the Thunderbolt issue. (My Tower is 2009, 8 Core 2.93, the iMac is Quad Core 3.4 i7) Had to encode things recently and it was quicker for me to network the Tower through the iMac to the Thunderbolt drives via Ethernet to have the Tower do the encoding, then the iMac doing the encoding. (Again, some of this depends on which app, how it uses multi cores and the rest.)