Yes, the GPU will speed up the simulation of fiber propagation calculations (these use the split step Fourier method and involves the frequent use of FFTs -> the FFT calculations are parallelized in the GPU)
The i7 will slightly speed up the overall calculations as a large number of double precision calculations are continuously run by the software. A faster clock speed will always helps for these types of sequential calculations. The RAM allocation will not directly increase the speed of calculations however it will ensure the stability of the software when large data calculations are performed. Large data sets can result in freezing of processes (due to memory issues) and may force the SW to shut down. A RAM allocation of >8 GB RAM will greatly help in this regard.