When my dell was made, the rule of thumb was the inspiron was the 'home' system, latitude the workhorse 'business' unit with different processors and dedicated graphics cards to suit, and the xps came along later as a gaming machine.
For engineering he'll probably need CAD which requires a decent amount of memory and graphics... Our CAD guys got new machines within the last couple of years with 8 core CPUs and as much or more memory - the sky's the limit I think.
The physics is theoretical but the fun is real.