MBP 2.3 GHz vs 2.6 GHz

I'm considering the 15" Retina. I presently have the 2.5 GHz Intel Core 2 duo with 4GB ram and has been good for my D700 capture while using PSCS3 and Aperture 2.

Within the next few months I plan to purchase the D800 and suspect the upgrade will be unavoidable due to the increase in file data. How significant is the difference between the 2.3 and the 2.6 quad core. There is a $600 difference and I'm wondering if it would be worth it. I don't do a huge amount volume as would wedding or sports photographers.

Also, if I were to use the D800 on my present system would it just be a slug?

Thanks