Today you want more than one core as one could run the application and the other for other things like the operating system.
As folk tend to have a lot more apps open, the more cores the smoother the work.
And if you use PhotoShop or apps that use more than one core, more cores can result in less waiting.
-> But there is no one that will tell you that something will do seamless, smooth work on HD Video Editing. I've seen big desktops with all the latest still drag as you work on HD Video.
Certainly you'd be looking at some i7 desktop for this work.
I'm in the market for a new computer and I haven't bought one for 8 years. I haven't kept up on the technology very well either so I'm unaware of what is needed for what, etc. Basically, I want to be able to run CS6 and Lightroom 4 seamlessly with enough horsepower to batch edit hundreds of high res images in the background while I work on something else. I think what I'm really looking at is would the upgrade for the quad core be worth it or could the dual core handle this, but if there is anything else that is more important to make sure I can accomplish what I stated above, I'm open to suggestions. Thanks!