I'd say 4 years.
cpu is basically already their seeing as it's replacement is due in a few months, but most games are still console ports with low depand. It is only now that game manufactures are looking at PC again as they feel (well, they say), they have reached the limit of the hardware (consoles). But then given at least a 3 year turn around for software, that is still a while off yet. by then you would expect the better/new consoles to be out anyway.
For general use though, I suspect you can get near 6 years out of it. Espically as a SSD gives a responsiveness far inexcess of CPU power.
On a side note. If buying a new house and need that upgrade money to make ends meet, I think your oversteaching yourself somewhat. If just for extra re-payments, then I withdraw my comment.