I am curious do you actually NEED a gaming laptop? The reason I ask is its usually cheaper to go desktop and you get better parts. You could buy a laptop for mobile use and build a sweet system for less than a gaming laptop.
Also note that models on GPU are very different from laptop to PCs you can't compare the models as equal.
Example being a GTX 260 vs GTX 260m wont perform the same.
No. Mostly it's a power saving feature. You don't need it to be running at 3ghz when you are on battery and just browsing the internet do you?