I found http://www.pcworld.com/businesscenter/article/228276/maingear_announces_3d_laptop_with_48ghz_processor.html which talks about a 4.8 GHz processor for laptops.
If you follow the link to the Maingear site, the fastest processor they offer is the Core i7 2920XM, which has a stock clock speed of 2.5 GHz. They require that processor in order to overclock it, and while they say they'll overclock it, they don't promise anything about 4.8 GHz. If it has a fully unlocked multiplier, they might be able to push it to near 4 GHz without using any more power than the video card does. Of course, that's because that comparison is to the hottest laptop video card ever. And I mean "hottest" in the bad sense of the word.
They'd have to use a different motherboard from normal, in order to be able to feed more power to the processor. They'd also need a strong cooling system. But if you make the laptop thick and heavy enough and the fans noisy enough, they can more or less keep it adequately cooled.
For some halo products like this, the real point of the product is to get some publicity, from news stories and forum threads like this one. If you hadn't previously thought of Maingear today, then you have now.
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It also depends on your budget. For a gaming laptop on a $2000 budget, you should definitely get a Radeon HD 6970M. Ideally, you'd like a Core i7 2720QM, but may need to accept a lower bin Core i7 2630QM for budget reasons. The higher bins above 2720QM are too much more expensive for not enough more performance. It would also be nice to get an SSD instead of a hard drive, but that may be impractical if you need a lot of storage space.
If you need long battery life, then you're really in a bind. Gaming video cards use quite a bit of power at idle, which zaps the battery pretty fast. In a desktop, it's no big deal for a video card to use 10-15 W at idle, but in a laptop, that's a problem. Both AMD and Nvidia have switchable graphics to turn off the video card and use the Intel integrated graphics, but that doesn't seem to get implemented with higher end video cards.
If you want a gaming laptop and also need long battery life in the same laptop, then you should wait to see what AMD's upcoming Llano APU offers. It might be possible to pair a Radeon HD 6970M with the top bin of Llano, and switch between the discrete video card and integrated graphics very smoothly, so that you can power down the video card entirely when it isn't needed for gaming. I'm sure AMD would love to have that sort of switchable graphics; it's really just a question of whether they can. But it should be a lot easier to make it work right when the same driver controls both the integrated graphics and the discrete card than when the discrete card has to decide whether to take over without having the slightest clue what the integrated graphics chip is doing internally.
Hopefully AMD would be able to offer more aggressive CPU clock speeds while turning off the integrated graphics. If the entire APU has a TDP of 45 W, then without the graphics, that should be able to handle four Llano cores at 3 GHz or so. That won't catch a Core i7 2720QM in performance, in spite of the higher clock speed, but it would be in the same ballpark. If a lot of the TDP is reserved for the graphics, so that with the graphics off, the chip can't use more than 25 W, then Llano could be rather bad for higher end gaming laptops.
Sager, Eurocom, and Alienware all sell the hardware that I describe in the first paragraph of this post. Asus and MSI don't yet, so I'm not sure if they're just taking their time, or if they think it will make more sense to pair parts with Llano rather than Sandy Bridge for a higher end gaming laptop. They surely know a lot about Llano performance that we don't.
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My recommendation:
Don't get a gaming laptop. Even if you need a laptop and also need a gaming machine, it's often better to buy both a cheap laptop and a gaming desktop than a gaming laptop. In fact, that's what you should do unless the whole point is to have a gaming machine that you can take with you when you travel, and play games on it when you travel.
Not to mention desktops offer more "bang for the buck", don't have the heating issues, MUCH easier to upgrade, etc.