If it's calculation intensive, it's unlikely that the difference between Mac and Windows are a factor 2. But it's worth a benchmark, if the Mac shop is willing to run the program for you (you might be able to find anotheri7 Windows laptop yourself).
My brother is looking to buy a laptop for his PhD. He has an application which is very intensive in calculation (SWAT) and may take upto 3 hours on his current lenovo (AMD) laptop.
Our choice was a Mac with i7, Quad-core, 13/15 inch, 2.9GHz, 8GB RAM. But this costs almost 1.52 lakh INR in India which is very costly.
However other brands with i7 like HP/Dell , as per his hands-on over a friend's laptop, did not match upto the speed he required but were priced around 70-80k INR. Now that he is a student and without any loan, is the Mac we have zeroed in on worth the price? This will be the first Mac we have ever purchased