How do I tell if a new computer will be better?

I_have_spoken

You should look at cloud computing like Amazon's offering to rent CPU as needed to run number crunching routines.

Mr_Toad

I doubt a new PC will give you much of a performance increase.

However, there are several things you can look at with the main one being the software and programming.

Is the Python stuff you're writing making full use of all the CPU cores/multithreading?

Is your code as efficient as it can be? There are many ways to get the same result but the difference between poorly written algorithms and efficient algorithms is vast. You only have to look at a few sort algorithms to see what I mean.

Have you considered another language?

Others have mentioned C and it's derivatives but you might want to look at something like FORTRAN, it's an old language but it still has a place for number crunching.

Also have a look at MATLAB this is designed for data analysis and number crunching.

There may be other suitable number crunching languages out there.

Do you have to run your programs on your PC or can you get access to a server that can do a far better job? I used to do some serious number crunching but I used servers with multiple Zeon CPUs and huge amounts of memory.