Do i need any additional cooling system if i overclock the 5770?
Not at all, though I would suggest a nicer card, such as a MSI Hawk R5770.
As for the 5830,
At peak loads many early reviewers saw wattage similar to the 5870, pcb revisouns have likely fixed that, but nonetheless it still uses much more power than it should for the performance it renders in games.
Mining is a different story however.
I have two that generate around 520MHs in total on a 750W PSU.
The Q6600 is a hungry beast as well, I beleive it's TDP is 140?
