Advice on computer

Hello, any advice you could give me on buying a laptop would be very appreciated. I am going to be using it for work primarily, not for gaming. My work requires a lot of processing (Matlab & Mathematica kinds of things, also heavy use of giant Office files), and I need to be able to take my computer with me from work to home and on trips a few times a year.

My needs are a fast processor, lots of RAM, and fast disk read/write. I don't really care about graphics cards so much, but I initially checked the gaming laptop sites because they seem to always be on the bleeding edge of performance. I only tune in to what the latest hardware is about once every 2-3 years (when I buy another computer), so I am not completely up to speed on what is out there now.

I initially went to Dell because I have had decent luck there before (I'm on an XPS M1710 right now), but the Alienware line seems to charge a lot for the little alien head that lights up.  I eventually found my way to DS based on a number of websites and reviews.

I am thinking about the following for an S17:
i7 920 2.66 GHz
6GB DDR3 at 1066MHz
Main storage: 160GB Intel SSD
Extra storage: 160GB Intel SSD
No OS
Price: $4293

Given that I am willing to spend that much money (or rather, my workplace is), do you consider that DS configuration the best I can do in terms of performance?  Also, will going to a 940 or 950 processor make that much difference?

Finally, I'm a little unfamiliar with desktop CPUs being put in laptops, so I have another few questions:

What will the battery life be like on this kind of machine?  This is not a dealbreaker for me, but I would prefer if I could work for 1.5 hours or so on a plane.

To use some language I saw in a forum somewhere, will this machine char my thighs?  Can I actually set it on my lap and use it, or will it light me on fire?

Thanks a lot for any help on this.  I realize that you probably get questions like this all the time, but I really only am able to tune into this community every few years and can really benefit from the experience of those who are lucky enough to be able to stay connected.

I guess I should also mention that this machine needs to last me 2-3 more years, and I am sure that I will use at least 200GB, maybe 300.  Are you saying that I should use a standard HD for the second drive?

thanks a lot for the input.  it's for storing data that i use a lot, so i will probably keep the SSD.  they are definitely expensive though.