The 6450 (DDR3 Version) ONLY uses 8 watts @ idle and 25 Watts at max. Which would be a much better choice given your PSU.
http://www.techpowerup.com/reviews/Sapphire/HD_6450_Passive/25.html
Didn't see manuf, Looks like a Liton (made for HP).
These are generally low-end PSUs. Manuf specs are always suspect on these PSUs as the ratings are at ambient temp and often as the PSU heats up deregulation sets in and you may only get about 60->80% of manuf spec.
For continous operation I would consider max avail power for +12 V rail at 116->135 Watts
Above 116 Watts Usage (12 V Rail) - can any one say Russian Roulette or Crap shoot.
The PSU may last 3 years, then again it may last 10 Min under a heavy load. If it goes you also take a chance that (unlike quality PSUs) it may take part of/all of remaining components.
My Recommendations on PSUs is that if not a tier 1 or 2, do not run above 50% of rated Manuf specs.