Most likely Spek has a 7xx series chipset - i have no idea how the southbridge (standard PCI-E 2.0 controller) would effect the performance...
For full-hd playing, the 1GB RAM is enough, above that the GPU would be too weak anyways.
Also, speaking about full-HD and high settings, he is most likely to run into a GPU limit, or at least a mixed limit. So an i7-7850 combo wouldnt be much faster than a Phenom-7850 pair unless he is playing in 900*1600.
Of course, he could build a completely new setup, with an i5 and a 7970, from 900$, only to see about 40-50% improvement from the 180$ 7850 what would already double his frame rates compared to the GTS 450.