Hwlp me decide on new laptop

I am engineering grad student, looking to buy laptop.
I am considering 2 following options right now.
1) Lenovo y470p ideapad (i7 2670 quadcore) known for amazing performance
2) Thinkpad t420 (i5 2430) , known for good performance and great durability

I am open to consider similar brands
1. What is your budget?
800-900$
2. What is the size of the notebook that you are considering?
14
3. What screen resolution do you want?
1600 by 900
4. Do you need a portable or desktop replacement laptop?
portable
5. How much battery life do you need?
minimum 3 hrs
6. Do you want to play games with your laptop? If so then please list the games that you want to with the settings that you want for these games. (Low,Medium or High)?
No
7. What other tasks do you want to do with your laptop? (Photo/Video editing, Etc.)
I run heavy engineering apps like Matlab.
8. How much storage (Hard Drive capacity) do you need?
anything above 200 Gb is fine
9. If you are considering specific sites to buy from, please post their links.
Nothing specific
10. How long do you want to keep your laptop?
Minimum 3 years
11. What kind of Optical drive do you need? DVD ROM/Writer,Bluray ROM/Writer,Etc ?
DVD ROM/Writer
12. Please tell us about the brands that you prefer to buy from them and the brands that you don't like and explain the reasons.
Prefer to buy - lenovo , Dell
13. What country do you live in?
US
14. Please tell us any additional information if needed.
The application which I run every day is Matlab. Some of my codes take 7-8 hrs on my present dual core processor. I wish to bring that time down as much as possible. I do watch lot of HD videos too. So in these 2 aspects, I wish to know how much of performance difference I can find between i7 quadcore and a i5 dual core.
Is it worth putting money on ideapad with i7 quadcore instead on the thinkpad with i5 which is far more durable?

Thanks