To quad-core or not to quad-core, watt(s) is the questions

I've been thinking of getting a new home computer and even considering getting a retail one from Dell vs. building it myself as I did last time. The reason I did a home build system last time was because I wanted tight control to make it as quiet as possible, and that off the shelf systems just didn't have the specs I wanted at the price I wanted. Last time I spent about $2000 in total, but this time around I'm looking for a sub $1000 system.

In fact Dell has just dropped their price on quad-core processors, reflecting the recent drop in price from Intel so I can actually get such a system for around $900 (assuming I can find a $350 off coupon that works - the current one is "sold out", ie. too many uses). That is pretty amazing since it also includes 2Gb of 800Mhz memory, and a 8xxx series nVidia graphics card. So I'd be getting a new system with a processor that has four cores each as fast as my current system for less than half the price.

But once again I find myself in a system specification quandary. You see I've been on a "low power" jihad recently, measuring the power consumption of all my electronics in a vain attempt to get my average consumption to less than the current whopping 1kw per hour. I'm not sure how that happened, but the reality is really high power bills! I know that an always on computer doesn't help - my current system sucks down 138w when idle, and 174w when pegged - combined with sundry peripherals that's probably 200w worth of power being drawn 24/7/365 which adds up to around $200 a year even at the cheapest rate. The reality is since my baseline usage is > the PG&E's minimum of 342kwh per month then most of my power costs me 20 and 30 cents per kwh, so actually system running costs are more like $400 to $600 a year!

What I do know is my Dell Inspiron 700m laptop sips around 18w when idle (and the screen is off) or a max of 41w when pegged (but not charging the 65Whr battery). That's impressive and I know that the latest laptop processors can probably do much better. So, do I try and build a state of art low power system or just go with the quad-core system and try to keep it off as much as possible? Or is there some happy compromise?

I know for a fact that the Q6600 processor I'm considering has a minimum power consumption of 50W currently, but there is a new "G0 stepping" version just out that reduces that to just 24W (see Extended Halt Power figures) although I know you still have to add all the motherboard, graphics card and other overheads before you get a true idle figure. If I'm really going to true low power than I'm either looking at Core 2 Duo laptop processors (of the T6000 and 7000 series) which idle at around 13W or in "Enhanced Deeper Sleep" mode go all the way down to 1.2W. As it turns out the standard desktop dual core processors now have an extended halt power of just 8W - that applies even to the top of the line E6850 processor.

The reality is I have a feeling that motherboard, graphics card and peripheral power usage will be something I have little control over and will probably far exceed the 20W variation I'm looking at in bottom line processor power consumption. So I think its going to be really hard to design a complete system with any assurance of what its total power consumption will be.

For this reason I think I'm going to focus on reducing my system's up time allowing it to go into suspend or even hibernate mode for more of the day. My current webcam monitoring system requires my system to be up 24/7 and my backup system keeps it occupied at least from the hours of 2am to 6am. The system is also a PVR and spends a few hours a day recording HDTV and recompressing it MP4 format. I'm hoping that eventually it can get down to only 1/3 of a day uptime which would probably dwarf any savings I could get by selecting a dual core over a quad core processor.