7200 rpm or SSD?

I'm looking to build a Macbook Pro over the next few weeks and I'm just looking at where to spend my money best. I will be getting the 15inch with i7 processor and upgrading to 8mb of RAM. My question is this: I understand the SSD is faster than the standard hard drive and will considerably speed things up in terms of processing pics etc. But how will the SSD compare to the upgraded 7200 rpm hard drive? The SSD are so costly for the size and I just don't know if I can justify the difference in price if the 7200 rpm drive will suffice (along with the upgraded RAM of course).

Any input would be appreciated!

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My Website: http://www.elmsphotography.ca