Silly whats a better setup question

[Josiah]

So I used 3 different systems the other day. All OEM.
System 1: Pentium D 920 2 GB
System 2: Pentium D 820 512 MB
System 3: Pentium 630 512 MB

I put them in order of most responsive to least responsive. I did basic stuff (browse through some pictures, open programs) System 1 was super quick, much noticeably faster than the other 2. System 2 and 3 were almost identical when it relates to responsiveness but system 2 seemed faster. What I am wrestling with in my mind is the cause behind system 1 being so much snappier. Is the RAM making that much difference or is it the extra cache and the dual core chip? I say it is the RAM because I saw improvement in my system when I upped the RAM to 1GB. I am sure the cache and dual core helps but how much?
I am building a HTPC and want something snappy. I am currently using a Pentium 550 with 1 GB. I will be keeping my main rig and building an entirely new one. At first I was going to get the same setup I am using but after using that thing I am having second thoughts.
Tell me your thoughts.

 

[Tutelary]

if you're building a HTPC you're going to want the dualie for the simple fact that a dual core can decode stuff like H.264 on the fly.
The answer to your question tho is most likely the ram. I noticed quite a difference going from a 1 to 2 gig even having a dual core cpu already.