How much faster is nVidia GTX 550 than GTS 250?

Okay I have a lot of questions… I currently have the nVidia GTS 250 (1GB). I am thinking about upgrading and want to know how much better the GTX 550 is.
1.) How much more processing power does it have?
2.) Is it any better than the 250 for processing distributed computing type programs such as folding@home?
3.) Also, would it be better to SLI a graphics card with my current GTS 250?
4.) Can I SLI a 550 with the 250, or must it be the same?
More info about my computer is above my signature…
Here’s info on the 250 GTS:
Field Value
Graphics Processor Properties
Video Adapter nVIDIA GeForce GTS 250
BIOS Version 62.92.7D.00
GPU Code Name G92GTS
PCI Device 10DE-0615 / 0000-0000 (Rev A2)
Transistors 754 million
Process Technology 65 nm
Die Size 315 mm2
Bus Type PCI Express 2.0 x16 @ x16
Memory Size 1 GB
GPU Clock (Geometric Domain) 602 MHz (original: 600 MHz)
GPU Clock (Shader Domain) 1566 MHz (original: 1566 MHz)
RAMDAC Clock 400 MHz
Pixel Pipelines 16
TMU Per Pipeline 1
Unified Shaders 128 (v4.0)
DirectX Hardware Support DirectX v10
Pixel Fillrate 9632 MPixel/s
Texel Fillrate 38528 MTexel/s

Memory Bus Properties
Bus Type GDDR3
Bus Width 256-bit
Real Clock 900 MHz (DDR) (original: 900 MHz)
Effective Clock 1800 MHz
Bandwidth 56.3 GB/s

nVIDIA ForceWare Clocks
Standard 2D GPU: 300 MHz, Shader: 600 MHz, Memory: 100 MHz
Low-Power 3D GPU: 600 MHz, Shader: 1566 MHz, Memory: 900 MHz
Answer #1
Don’t get a 550 if you have a 250 unless you need DX11.
If your going to spend money on an upgrade, get at least the GTX 560 (or 460)..!
Answer #2
good spec comparison site for vid cards
http://www.techarp.com/showarticle.aspx?artno=88
a a benchmark site
http://www.videocardbenchmark.net/
seems the GTX 550 is much faster than the GTS 250
Answer #3
check it all Nvidia card specification compare and price.
http://www.nvidia.co.uk/object/geforce_family_uk.html
Answer #4
http://lmgtfy.com/?q=gtx550+vs+gts250