UPS is not the problem here.
And, I don't think his system draws about 350W or more. Even with a power supply of 600W, it does not
mean that whole system takes in 600W. It's just saying that it can provide that much power.
And Even Your VGA NEEDS 450 Watt or greater power supply
AMD's website just overrates the power requirements of a card.
Actually, a HD 6750 only needs a 350-400W PSU. ( if the makers of the PSU are good, i.e )
I've seen HD6850 running on an Antec Earthwatts 380W PSU.
So, this isn't a problem with the UPS.
Does those games,
nfs undercover,pop the forgotten sand,pes 2011
crash as well after an hour ?
If so, I think it's an overheating issue.
You should check the temps on that card.