The biggest difference is features. The 6950 supports 3 displays with a single card, 560 does not.
i series breakdown
i3 = hyperthreaded dual core... 2 physical cores, 4 logical cores ( shows up as a 4 core in performance monitor) includes anything below a 2400
i5 = standard quad, 4 cores in windows 2400 to 2500k
i7 = hyperthreaded quad. 4 physical, 8 logical, shows up as 8 core in windows. 2600 to 2700k
Just the CPU, popping in your own chip is easy, just line up the notches, and flip the bar into place. The motherboard you purchase (should be a p67 or z68 chipset, avoid h67/h61 for high performance machines) should give you a step by step guide for the install.
I'll get back to you on price ect when im a little better off financially, i'm thinking around december is most likley. It might be a bit in shipping over to you in the old world.
Corsair is an awesome brand for PSU's.
Windows 7 Kicks a**....
SSD Pro and CON
Pro
Fast
How fast? DAT FAST. no lie...
Fast...
Con
Money
size
Gigabyte == Win, Asus == Mostly good, ROG == Poop in a bucket, ASRock == good for budget minded. Look at size, case, planned upgrade path.