It does have the best i graphics, but thats mainly for 3d rendering speed, not anything you'll notice. The difference in speed between the quads is minimal, but then so is the cost. I'd go for the 3570k, you'll get the quad cores, you'll get the best igpu (even if you don't use it), and you get the fastest clock speed for not much more than the slowest i5. I would stay away from a dual core, even if its just for responsiveness reasons. If you are looking to save any components from your current build, make sure that the mobo you buy has IDE if you are intending you use your current HDD's (assuming they are ide of course), as most only have sata.
personally i'd go for a low-mid range atx mobo (not matx, so you have 4 ram slots), reuse your case, get a new psu (just in case), new HDD (x2, one from OS one for Data/backup of images, store each image on two HDD's), new OS (64bit win7), 2x4GB of ram (maybe 16GB as its cheap), and the 3570K.
Sounds ideal. I am planning on paying NCIX her $50.00 and let them build and set Win, I would sooner let someone else deal with drivers etc and all the updates.
As my existing Computer will stay as is and used as a back up I will probably just go with one drive and network all my back up images to the old company in case something went wrong. Any suggestions on what mobo to pair the 3570K with. Any point in getting a case with some USB3.0 on? Is 3.0 used with anything.
Here's what I had been thinking. I picked that mobo because NCIX here have it bundled with the 3570k for $349.99 with a $20 mail in rebate. http://pcpartpicker.com/ca/p/ekhp