New machine

For development - and my experience is VS2010 - almost anything will do. I am still happy with Windows 7-64 and 12GB RAM on my (now 3 year old) Core 7.

The area that frustrates me is disk access for external drives. I would suggest this is the area that requires most careful invesitgation.

The biggest way forward is getting more parallel processing running and getting processor levels above 10%

Thinking along these lines at the moment with a 180GB SSD

http//www.overclockers.co.uk/showproduct.php?prodid=FS-249-OE

i7 Ivy Bridge processor
Motherboard with dual Ethernet Gbit ports
Write blockers (one internal in 5.25" slot, external USB 3.0/eSATA)
Ports, ports, ports (Thunderbolt, USB 3.0, eSATA)
Synology DS412+ NAS with a D-Link DGS-1005D switch

All that should run less than $2k; $3k with hard drives

Write blockers (one internal in 5.25" slot

I specifically recommend against this. It's nice, but it's a cost blowout when I have a pair of eSATA writeblockers. I can switch these between my primary and secondary exam workstation as needed, and take them out for field acquisitions as needed. Internal write blockers limit your usage cases.

Of course 2 more cables and a box on my very large workspace for examinations does take up some negligible amount of space and doesn't look as pretty as an internal.

Also, big props on using an SSD for your case database. I use one for my FTK3 DB and very much enjoy the user experience of fast filtering and sorting the file list.

I take it you already have a dedicated RAID card that you can re-use?

I have an Antec TwelveHundred (12 bay) and although I love it for cooling, it's not as easy to swap drives as I'd like. I say that about a lot of cases. I loved the bottom 4 bays in the old Antec Sonata case that mounted sideways so you could pull them in an out quickly, but I always need more than 4 bays.

Write blockers (one internal in 5.25" slot

I specifically recommend against this. It's nice, but it's a cost blowout when I have a pair of eSATA writeblockers. I can switch these between my primary and secondary exam workstation as needed, and take them out for field acquisitions as needed. Internal write blockers limit your usage cases.

Let's agree to disagree, Tony. I currently have only 1 internal write blocker, but it is by far my favorite piece of equipment. It's a direct SATA II connection to my motherboard, so it's noticeably faster than my eSATA write blockers; plus, it also write blocks USB devices. And the internal one cost me less than my external ones. YMMV

A good SSD and dual screens will do more for productivity than a slightly faster CPU.

My current machine is,
Windows 7 (64-bit),
Intel i7-3820 CPU @ 3.60GHz, <== Excellent
16.0GB DDR3 RAM, <== Why get any less?
ATI Radeon HD 5450, <== Rubbish, but low power
Intel 520 SSD 240GB, <== Excellent
Gigabyte X79-UD3 Motherboard <== So So, it is a bit buggy

Just built one with an ASUS mother board - http//usa.asus.com/Motherboards/Intel_Socket_2011/P9X79_PRO/
with an i7-2600K.

G-Skill RAM - F3-19200CL10Q-32GBZHD 32GB(4x 8GB)

In a pretty quiet Antec case - http//www.antec.com/product.php?id=2743&fid=6

But the biggest performance boost came from an OCZ Revo drive - http//www.ocztechnology.com/ocz-revodrive-x2-pci-express-ssd.html

Just built one with an ASUS mother board - http//usa.asus.com/Motherboards/Intel_Socket_2011/P9X79_PRO/
with an i7-2600K

Multiple USB 3.0 and eSATA ports - excellent. But where's the Thunderbolt?!! wink

A good SSD will be the most noticable improvement you add to your PC - but there are a lot of SSD's out there. As a general rule of thumb, don't get an OCZ SSD and the newer the SSD the better.
The cheapest improvements you can make are a second monitor (which is pretty much essential), more RAM and a better graphics card. A lot of examiners underestimate the amount of work the graphics card does, especially in processing the millions of thumbnails you'll have to go through.
Once you've got those, pretty much any system will do.