Go with the 7.0. I acquired a 5cf for free. It holds 3 kegs and the cO2. If I put the cO2 on the outside, I think I could put a 3 gallon keg on the hump. Mine works great. Of course I added a collar and painted it black.
I'm happy with it but it was free...bigger is better.
The 7.0 GE from home depot fits 4 on the floor. A bunch of people, including myself, bought them over the holidays for $160 delivered. In the process of converting mine this week.
2 kegs, 5lb CO2 with dual reg, computer fan, Johnson A419, six pack on the hump, and basket for miscellany. Perfect for an apartment and my frequency of brewing/drinking. Collar and taps soon.
Keep in mind that even with the coarse adjustment cranked all the way up, it still stays below 30deg. You will need a temp. controller. Any questions, feel free to ask.