M3 vs M4 and 256GB vs 512

Hi everybody, For a bit of context I'm a student with 1 year left in my master's. I want to do computational chemistry / bioinformatics (PhD). My current computer is old and heavy, and though it currently can do what I need to do, it's kind of a pain to carry and very slow.

I'd like to buy a MacBook Air. I think M4 chip would be nice if I need to run some computations on my personal computer. What I'm mostly worried about though is the storage. It would be like 300€ more to upgrade from 256 to 512. For the type of work I'm doing, I obviously handle a lot of data but I should also have access to a cluster most of the time, so I wonder if 256G + hard drive would be better.

Also if I have access to a cluster I wonder what the real advantages of M4 over M3 would be ?

Thanks :)