Ideas for efficient multitasking workstation built on two Xeons

I am looking for the machine as follows:

APPROXIMATE PURCHASE DATE: the closer the better, BUDGET RANGE: (example: 3000usd)

SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: scientific multiprocessor computing, multitasking workstation (normal work + running computations in the background), openGL programs (but no gaming), applications supporting nvidia cuda

PARTS NOT REQUIRED: keyboard, monitor, mouse, speakers, OS

PREFERRED WEBSITE(S) FOR PARTS: newegg.com (but I'm buying it in Poland)

PARTS PREFERENCES: Intel cpu + NVIDIA graphics

OVERCLOCKING: No

MONITOR RESOLUTION: not applicable

ADDITIONAL COMMENTS:

My idea for such workstation:
Processors:
2x
Quad-Core Intel Xeon Processor E5405 - 2,00 GHz; 12MB cache
http://www.newegg.com/Product/Prod [...] 6819117151
Motherboard:
Intel Workstation Board Veronia S5000XVN - 6xSATA - PCI-E x16
http://www.intel.com/Products/Work [...] erview.htm
Memory:
8x Kingston 1GB 667MHz DDR2 ECC Fully Buffered CL5 DIMM Dual Rank
(or better 4x 2GB?)
Storage:
http://www.newegg.com/Product/Prod [...] %207200.12
graphics:
http://www.nvidia.com/object/produ [...] 85_us.html
box and PSU:
Intel SC5299 BRP Pilot Point 4 (650W)
http://techmall.biz/intel-server-c [...] -3168.html


Alternatively I am thinking about more expensive configuration:

procesor 2x Quad-Core Intel Xeon Processor E5504 - 2.00 GHz

motherboard Boxed Intel® Server Board S5520SC

memmory 8GB Kingston DDR3 2GB 1333MHz ECC CL9 with Thermal Sensor

storage Seagate 1 TB Barracuda 7200.12 (32MB, Serial ATA II)


graphics GeForce with CUDA GTX 285 Asus 1GB 2x DVI (PCI-E)

box/psu Intel SC5650 BRP (600W)

Sorry for links from different sources and no links in the second solution, but I am not asking about exact prices or where to buy it.

I wonder whether these configurations are OK
* whether all parts are compatible, (I think they are, but I am quite newbie in this stuff)
* whether some part is not bringing down performance of another one
* whether there is another configuration that is cheaper but still has as good performance

Thanks in advance for any help

I will buy the machine in Polish shop. I posted the links just that readers have quick access to specs for the parts.

I have no idea about overclocking so maybe I should not do that ;-) Now I try to make a configuration with faster Xeons from 5400 series, with help of a friend. I should have a space for that in my budget, as he suggested me cheaper solutions for a computer case (the one I selected is for servers).