Uhm time out!!!! I do NOT agree that a PSU with 16 amps will run a 9600gt. I've got a slightly overclocked 9600gt and it wanted 26 amps if I'm not mistaken. The 4670 would be the best of those 3 for a low power solution. It's about the same speed as the 9600gso, but requires no power connection. So probably best card I would personally take a chance on with a psu like that.
As far as temps, if you are concerned with that, what I did when I got my 9600gt was to get a high flow pci slot cooler fan and mounted in the bays below the card that way a lot of hot air should be pulled off the card and sucked out the back of the case. Might be a good route to go for little cash.
As far as the 9600 gso card, if you do go that route, check the specs as most of them lately seem to be ddr2 cards which would be crippled compared to the other cards your looking at.