I definitely agree with the recommendation to look at the Mac Performance Guide.
Another option that you didn't mention is to get a Mac Pro with a 6-core 3.3 GHz Intel Xeon "Westmere" processor. It will be faster than the options you mention. Not many applications relevant to photography are capable of using 8 cores -- most can't use more than 4. A few can -- DxO seems to use all my cores when processing a batch of RAW files (I have the 6-core 3.3 GHz processor model).
The most important recommendation for your size files would probably be to have lots of RAM. As much as you can afford (or as much as will fit into the machine). And, as mentioned, don't buy it from Apple. OWC is a commonly used source for Mac RAM (and other items). Others sources are available. A potential advantage to the dual processor machines is that you can install 8 RAM modules, rather than the 4 you are limited to with the single processor models. I believe 8 GB RAM modules are the largest available now, so with the single processor machines you could have a maximum of 32 GB of RAM. You would have to remove the Apple-installed modules and install your own 8 GB modules to get to that point. I have 12 GB of RAM in my machine, which seems enough for my usage (and my file sizes).
The 3.3 GHz option can be found (if you haven't noticed it before) by selecting the Quad core option at the Apple store and looking at the processor options.
There are rumors of a new Mac Pro model to be announced soon. You might check the forums at www.macrumors.com
or elsewhere to read more about that. These are just rumors at the moment. If you need something now, probably buy it now.