Intel i 7 quad core processor compared to core 2 duo

i'm looking at a Dell laptop and need info about the i7 720QM, vs. i7 820QM or instead, using the core 2 duo p8700.

What will be the real difference in actual performance for home use with each of these CPU's, minimal gaming, but Office 2007 and AUTOCAD 2008?

Very noticeable in autocad, minimal in Office unless you have a habit of working with gigantic excel spreadsheets (in which case the i7 will be faster).

I'd get the i7. It probably isn't worth the money for the 820 over the 720 though.

Well, there are a couple of times when I'd lean towards a core 2. For a fairly thin and light 15", where cool running and battery life are priorities rather than raw processing power, I'd tend to lean towards a P series (25W TDP) Core 2. For performance though, there's no question. Get the i7.

The mobile i7s shouldn't have half the battery life - the TDP is only 10 watts more, and they dispense with the northbridge. I would expect their battery life under load to be a bit less, but due to the capability to shut down cores and the significant power saving capability, I wouldn't expect the idle battery life to be much different from a Core 2.

Higher power consumption does not mean greater battery drain either. One has to look at efficiency to get a more accurate metric. If the i7 does 2.5x the work in the same time but draws 15% more power (just pulling numbers out of the air of course), it will finish much earlier and switch back to idle where it draws very little power, while the Core 2 will keep on draining the battery as it struggles to keep up. It will drain the battery faster, no doubt about it, but it will drain for alot less time.

Thanks to everyone for the input. I will be on AC much of the time so battery life isn't as iimportant as having the raw power when I need it. I decided to go with the i7 820 QM even though it cost more. I didn't need to buy another copy of Word which partially offset the extra cost.