I don't have recommendations for laptops or specs, and I'm not in OB. But have you checked how things works in your department? Because maybe you need take that into consideration.
For example, I got a laptop from the university when I started my PhD. It's not a Macbook or any amazing laptop, but it can get most things done.
There are differences when I need to install software. My advisor uses SAS. If I need to install SAS in the laptop provided by the university, it's a lot easier since it's a university asset. I just take my laptop to the IT guys and they do it for me. I'm seen more like an employee who needs an equipment.
If I want SAS installed in my personal laptop, I need to follow a very different procedure, fill a form, request approval, go to another part of the campus, etc. I'm seen more like a student who wants a software.
Other students in the department use different software, and it seems they may have different challenges. I saw people using R and saying that they needed much more memory, for example.