Hi there and welcome to the forums:

Please browse the Chat Room and BOINC Support forums. There are many prior discussions on the same request. The very first question is: What is your budget and what level of technical expertise do you have [v.v. self builds].

Just got a [brand] 8 threaded machine [retail] at a steal price, using 79 watts hour when running at 2800 MHz and 60 watts when stock 2200 Mhz. It could even do 3100 Mhz, but the power consumption and temperature rise exponentially when doing so... it usually trundles at 2500-2600 during the day and 2800 during the night, in the cold room [the Hrz are atuo-regulated]. To me, for sure the Intel I5-I7 2xxx series such as the I7-2600 is the present choice CPU. The version I have has a measured 42 Watts/Hour CPU consumption, with a max of 45 [TDP is the given term in the Core-Temp tool]. Power is expensive here, so with that procurement, retired a 2 threaded 85 watts using machine and do about 5-6 times more production with the new. With that, the total TeraFLOPS contributed to WCG has nearly doubled [see my sig]. Imminently my 5+ years old Q6600 will also be replaced [using 170 Watts hour], by a second 8 threaded machine, to co-act as file server. The combined power saving will be the payback within the next 3 years, live expectancy 5-6 years, at 24/7 crunching. Much lower wattage is much lower heat generation and much greener at that, no matter how the power was generated.

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What they said:
Plus

I built three machines in December for Crunching: The current cpu chips are up to 10 times better than five or so years ago.

Short form: build something you can run 24/7, heat and juice bills permitting. I use Intel, Other CPU's are available:

i3/2100 CPU : dual core plus hyperthreading, very good, not overclockable. Cheap, fast and not power hungry.

i5/2500K quad core, no hyperthreading. Goes like a train and stays cool. Can be overclocked. mid price, faster than the i3 when crunching.

i7/ 2600K, quad core plus hyperthreading. Extremely fast, and not cheap. Can be overclocked for more heat, and more points.

Also, what you can do with speed settings depends on the motherboard, the cheap Intel ones work, but something like a board from Asus or Gigabyte gives more speed options. Spend money on cooling.

Running an i5 at stock speeds 24/7 gave 6700 credit per day in BOINC stats. Unbeatable at the price, I think. Stats for the i7 aren't in yet.

To help keep the price down, use Linux. Ubuntu is pretty simple but there are other versions out there. They are free to use. Plenty of folks to assist you to get started if you go this route. Try to get a quad with hyperthreading (8 threads). For a real nice machine, buy a dual socket motherboard. Start with one processor. Then save up for the second processor. This is provided you build it, or have a friend build it for you. A heck of allot cheaper if it's home built.

Dual boot it will shortly be on the new 8 threaded. Make your choice of Linux easy: http://www.ghacks.net/2012/01/04/download-lin...r-desktop-with-get-linux/

[CEP2 crunch under W7-64 is superior [in efficiency] to that under Linux [on any hardware that I have]

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edit: insert [in efficiency]

The note about W7 being faster than Linux ( or Brand X) is interesting. I don't have any answers as both my boxes (one of each ) have different CPUs. My attraction to UBU is its cost (£0), its low memory requirement, and its snappy front end.

It's nice to have the choice. I use W7 most of the day, while the Ubu box saves the planet from people like me.