[R] 8 fast or 4 very fast cores?

[Leif Ruckman]

I am going to buy a new computer ( Dell workstation T5810 - Windows 8) 
to work with simulatons in R.

Now I am asked what kind of processor I like and I was given two choices.

1. Intel Xeon E5-1620 v3 - 4 cores 3.7 GHz Turbo
2. Intel Xeon E5-2640 v3 - 8 cores 2.6 GHz Turbo

I don't know what is better in simulations studies in R, a few very fast 
cores or many cores at normal speed.

Can you please give me help about this?

Warm regards

Leif Ruckman