VPS 1 core vs 2 cores

[Keith Smith]

Hi,

I am wondering what your opinion is on cores and RAM when using a VPS.

I am thinking about this in the context of Drupal and Magento, both of 
who are resource hogs.

I was told more RAM is much more valuable on a VPS than is the number of 
cores.

I'm assuming 4G of RAM is enough to not go into swap.  I'm thinking this 
should be fine for a production site with moderate traffic running 
either Drupal or Magento.

As you know more cores means more money when it comes to VPS servers, 
while RAM is cheap.

Of course we know opcode cache, varnish, and memcache(d) can work 
wonders in speeding up websites. For this discussion lets assume we are 
using none of them.

The question is, will a second core make all that much difference if 
enough RAM is present to not use swap?  How would I know I need a second 
core - look at the load?

And is there other consideration or things I should be looking at?

Thank you very much for all your feedback!!

Keith