Dual processors vs more Cores

I am shopping for a Dell Precision T7610 Tower Business Desktop. I see a processor option to do either 2x4 cores or 1x8 cores (among many others, but I think it's one of these two choices). I have never seen that option before. Is there a difference in performance between the two? Interestingly, 1x8 is much more expensive than 2x4.