Processor with DMI bus type which has higher clock speed and max memory bandwith, or QPI bus type with lower clock speed and max memory bandwith?

Hello all,

Which is better between Intel Core i7-3930K and Intel Xeon E5-2620 for best computation performance in COMSOL?
Let's assume both using 64 GB of RAM.

I noted that Core i7-3930K has clock speed of 3.2 GHz, bus type DMI with 5 GT/s, 4 memory channels, and max memory bandwith of 51.2 GB/s
While Xeon E5-2620 has clock speed of 2 GHz, bus type QPI with 7.2 GT/s, 4 memory channels, and max memory bandwith of 42.6 GB/s.

What I really want to know is, does bus type DMI or QPI really affect performance better than higher clock speed and higher max memory bandwith?
If having bus type QPI is much more important than having bus type DMI with higher clock speed and memory bandwith, I think I will choose Xeon E5-2620.

What's your recommendation?

Regards,
David