Core I-7 860920, 945, 975, what is needed for everday use. I hear most the programes are not set to hand a quad processor any how ans still only run off one, that when multi tasking you may see more perforamce then presious runnning of a single processpr....thoughts???
It really depends on what you use your computer for. People who just surf the internet and listen to music might be fine with a single core. Most users, even gamers, will be happy with a dual core. Heavy multi-taskers/encoders/'hardcore' gamers etc will want a quad core.
And from the CPUs you listed the best for the price is a either the i7 860 or 920. You might want to look into other options as well (unless you aren't looking to purchase) such as i5 and Core2Duo, or on the AMD side, Phenom II and Athlon II.
The latest processors will give more frequency to the one or two processors in use and scale back on the processors not in use.
When all processors are in use, it give speed to all four.
It's called a "turbo" feature.