All of those you listed are excellent machines in their own right.
The Sentia is a great business/casual gamer laptop with very low batt consumptions and a super cool vibe to it.
The Area 51m is a desktop replacement...no two ways about it. Its big, heavy and has a huge screen. And a full blown P4 with a "user-upgradeable" video module that ATi and Nvidia have both agreed to support with their next generation of mobile video cards.
The M460 is a very well balanced setup as you posted. A powerful Centrino chipset coupled together with the latest and greatest from ATi is hard to beat. In fact, I'm seriously considering picking one up myself as I have need for one more laptop that is not at all like my Area51m (which I love
) that is just a bit more mobile as I travel 3-5 days every week, 52 weeks a year.
Just be sure to peruse all of our Alienware/Sager databases here as well as the Voodoo forums at www.voodoopc.com
and I'm sure you'll make a decision that best fits your needs...b/c no one knows what they are better than you.