My guess is the difference will be huge, but that's not guaranteed. The laptop is probably a dual-core and thermally constrained to < 3 GHz, possibly with less memory than it really needs. So it depends on what the performance constraint is. If it was running out of memory and using swap (admittedly not likely, unless the laptop is old enough to have < 4 GB), doubling the memory might chop that down to less than 1 hour without any other changes. On the other hand, if it is single-threaded stuff taking the time it might take re-writing that (whether Python code or Excel formulae) to make a noteworthy difference. Most likely there's quite a bit of multi-threaded stuff, so two or more extra cores would be great; the extra clock speed is always useful.
I suggest you get the specs of the laptop, and find out as best as possible where the bottleneck is – check memory usage, CPU usage and disk activity. A CPU usage of ~50% on a CPU with HyperThreading could still be a bottleneck.
Does he want something for gaming as well? In other words, do you want to spend a substantial amount on the GPU?
The thing with that system is you're paying for a $300 case, $230 PSU, $300 mobo and $250 CPU cooler. That's unnecessary – a $100 case, $150 PSU, $200 mobo and $50 CPU cooler would be just as good from a functional perspective. Not to mention, being a gaming system it has a $700+ GPU that won't help with the calculations unless they're completely re-written to use GPGPU (and that might not be appropriate).
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I may occasionally give advice regarding (consumer) law, but it is only my opinion based on my reading – I am not a lawyer.
Romans 3:23; 6:23; 5:8; 10:9-10,13