Well, let's take a look at the specs...
I have color coded the difference between the two PB's in question.
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$2,499.00
667MHz PowerPC G4
1MB L3 & 256K L2 cache
133MHz system bus
256MB SDRAM memory
30GB Ultra ATA drive
Combo Drive (DVD-ROM/CD-RW)
ATI Mobility Radeon 7500
w/32MB DDR video memory
Gigabit Ethernet
56K internal modem
1 FireWire & 2 USB Ports
AirPort Ready
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$3,199.00
800MHz PowerPC G4
1MB L3 & 256K L2 cache
133MHz system bus
512MB SDRAM memory
40GB Ultra ATA drive
Combo Drive (DVD-ROM/CD-RW)
ATI Mobility Radeon 7500
w/32MB DDR video memory
Gigabit Ethernet
56K internal modem
1 FireWire & 2 USB Ports
AirPort Card Included
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Now let's look at what you're gaining by going with the 800MHz
Price = $700
Processor = 133MHz
RAM = 256MB (512MB- 256MB)
Hard Drive = 10GB (40GB - 30GB)
AirPort Card = Included (not included with 667MHz)
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Now that we know all the facts, let's talk about it.
The price difference is nothing to scoff at. But let's not think of that right now. Let's look at the additional items on the list and go from there.
You should be asking yourself, Am I going to upgrade these items if I bought the 667MHz? (yes or no)
Processor - 133MHz
Not much of an upgrade here, honestly, I don't think you would see a massive speed increase, if one at all, with the 800MHz. I won't even ask you if you would have upgraded this item, I'll assume you wouldn't buy the 667MHz then upgrade the the 800MHz.
RAM - 256MB
Double the RAM. Consider that RAM lovin' OSX will be on this system. But would you have upgraded this item? (yes or no)
Hard Drive - 10GB
10GB more in storage. Just enough to make you wounder. But would you have upgraded this item? (yes or no)
AirPort Card - Included
Included with the 800MHz unit. And worth $100 after market. But would you have upgraded this item? (yes or no)
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My 2¢
Honestly, there's not much here tempting me to spend the $700 to upgrade. If you ignore the nominal items, such as processor and Hard Drive, you're really only left with RAM and AirPort Card. For $300 - $350 you could upgrade the 667MHz to include an AirPort Card and the additional 256MB of RAM.
But know this, I called the Processor and Hard Drive items becuase 133MHz is not that much faster and 10GB is not going to break the bank for storage. I have an 8 GB hard drive on my G3 laptop and I consider myself a power user. All of my heavy storage is done on my desktop.
The more I look at this, the AirPort seems to be the decision maker on this one. You have to ask yourself would you use the AirPort Card? Do you have a Base Station. If not, when do you plan on spending the $300 to get one?
These are important decisons because if you decided against the AirPort Card, you would be spending $100 in the upgrade that you didn't need to spend. It might be worth the $100 for you to have the AirPort option, and along with that some additional items you may talk youself into buying the 800MHz unit just for that.