Question: New computer for programming

I'm thinking about getting a new laptop (since the current one is kind of outdated). I use a lot of Matlab, Maple and Mathematica and will be doing come cfd computations. I found two laptops which, for the same price, only differ in processor and screen size. One features a i7-2620M and has a 13' screen and the other a i7-2670QM with a 15' screen. What I need to know is if the difference between processors is significant enough for me to turn a blind eye on portability (1.7Kg vs 2.6Kg and a large difference in battery autonomy). In other words, how significant are the differences (http://ark.intel.com/compare/52231,53469) between the i7-2620M and i7-2670QM for this kind of computer usage.

I've already read this thread:http://www.mapleprimes.com/questions/40949-Anybody-Tells-Some-Experiences-About but it didn't help much...