I would ignore what sastusbulbas wrote above becuase, well i don't agree..
Sure, why not, tell him to ignore someone ASKING if an i7 is overkill.
I see nothing to suggest an i5 or an AMD processor WOULD NOT suffice, nor where his demands are so high he needs an i7 with 16GB of memory.
Like usual, elitist PC snobbery gets in the way, and overkill is advised before anyone takes into consideration what will actually be getting done and how much time spent doing it.
It could be as little as 16 seconds three times a month ripping a DVD, or a few frames on a single 1080p monitor on old games twice a week after watching Friends or Breaking Bad. Well worth an extra £200 on performance which may never be utilized.
He states uses such as occasional gaming, movie watching and a bit of undisclosed video work, the sort of stuff which many use AMD for because it does not justify the cost or performance of Intel.
My son has my old 775 PC. Your claiming an AMD F6 6300 with a Sabertooth motherboard and 8GB of low latency 2133Mhz memory is not an upgrade over a Q9550 with 4x2GB of 1066MHz DDR2 on a Gigabyte GA-EP45-DS3P LGA775?
He plays games, watches movies and the various other stuff schoolkids do on a PC such as homework, HD video's, DSLR photo's etc. Nothing different to the OP I would guess. Does he need an i7 with 16GB of memory?