You can buy 1 bitmain u3 off amazon for $70 and get a better watt/GH return 60GH/s for 60watts
u3: 1watt/GH
7970's: 200-300watts for 0.6-0.7GH/s
And whoever is paying for electricity will notice a jump of that nature...
Each card would only do 700-740kh on scrypt mining.
Best bet is get a gaming computer for gaming, and a Bitcoin miner for mining.
Or he could mine X11 which would give a lot more..
Other algorithms does exist...
I would not recommend mining with a Gaming PC since the cards will take damage.