Today’s overdue Mac Pro update is a welcome change, but for a computer that’s so expensive, why not just get an iMac?

Here’s an attempt at configuring an iMac and a Mac Pro to be as similar as possible, in a high-performance configuration (yes, you can build a cheaper iMac, but this is for people who stress their hardware):

iMac Mac Pro Monitor 27” built-in 27” Cinema Display CPU 2.93 GHz i7 2.8 GHz W3530 RAM 8 GB (in 4 slots) 8 GB from OWC (in 4 slots) Max RAM 16 GB (4 slots) 16 GB (4 slots), or 32 GB with OWC’s 8GB modules Video card Radeon 5750 Radeon 5770 SSD boot drive 256 GB mediocre SSD 240 GB much faster SSD Second drive 1 TB 1 TB Hard-drive bays 2, inaccessible 4, easily accessible Max monitors 2 a lot Firewire ports 1 4 AppleCare $169 $249 As configured $3,487 $4,660 ($1,173 more)

I made some assumptions, like that you’d be willing to buy third-party disks and RAM, and that you’d be comfortable upgrading both in a Mac Pro (where it’s easy and intended), but you wouldn’t be comfortable upgrading the disks in an iMac (because it’s difficult, unintended, and has so much potential to damage the screen or get dust in it that even I refuse to attempt it). I also assumed that you wouldn’t care about the PCI-Express slots or extra optical bay in the Mac Pro, and that you wouldn’t find the dual-socket versions worth their premium, even though they give you twice as many RAM slots.

The Mac Pro will probably carry at least a $1200 premium over a similarly configured iMac no matter how you configure them. So the iMac is the practical winner for most people with average needs.

So why buy a Mac Pro?

I have a Mac Pro and Tiff has a 24” iMac. Both were purchased in early 2008. We both have high demands: I write a lot of code and process a lot of data and media files, and Tiff heavily edits wedding photo shoots with thousands of huge RAW files.

Now that both of our computers are nearly three years old, mine’s still doing fine for the foreseeable future (although I’ll put an SSD in it soon), but we’re ready to throw Tiff’s out the window.

My desk is clean and mostly free of cables and peripherals, but Tiff’s desk is covered in hard-drive enclosures. She’s using an X25-M SSD in a Firewire 800 enclosure as a boot drive, since the iMac’s internal hard drive is too slow. She’s using a pair of 1 TB disks in RAID-0 as primary storage, in another Firewire 800 enclosure daisy-chained to the SSD’s, because the iMac’s internal hard drive is too small. And she has another 2 TB external USB disk for Time Machine.

My Mac Pro has 4 internal hard-drive bays, so I don’t need any enclosures except for the occasional off-site backup disk. All of my disks are faster, quieter, and more reliable because they’re in directly connected, well-ventilated internal bays. And each one was cheaper, because I didn’t need to buy an enclosure to go around it. If I need more disks, I can add a PCI-Express eSATA card to connect an external enclosure at full speed.

Tiff’s iMac is maxed out at 4 GB of RAM, which is part of the reason she needed an SSD. My Mac Pro has had 6 GB for its entire life so far, and if I needed more, I could add another 4 GB for just $150 or spend more as needed to install up to 32 GB.

When we replace Tiff’s iMac, the excellent 24” monitor that’s built into it will need to be replaced, too. When we eventually replace my Mac Pro, I’ll be able to keep my monitors. (Possibly with an adapter, if the port has changed by then.)

If I splurge on an internal SSD, I can bring that with me to any future computers. If the iMac had an internal SSD, it would likely depart with the iMac to wherever its new home was.

And if we sold our computers, I’d get much more money for mine. My friend recently sold his single-socket, 2.0 GHz Mac Pro for just over $900 on Craigslist with local pickup. It cost about $2000 new… in 2006. A quick search indicates that we’d be lucky to get $600 for Tiff’s iMac (assuming we’d keep the external disks).

Especially because that excellent 24” monitor stuck inside of it is starting to flake out. And it’s out of warranty. When that monitor dies, the computer is worth almost nothing.

While the Mac Pro costs a lot more up front, high-performance users also get a lot more value and versatility over its lifespan, which is likely to be much longer and end much more gracefully.