simple googling for Computer Watt calculator would been easier then posting here .
http://www.extreme.outervision.com/psucalculatorlite.jsp figures ALL components then determines if your specific configuration is going to use alot of power.
IMHO I think your wasting your money. Your running DDR2 RAM (very slow) on a Q6600 which was a low end CPU back introduced in 2006 (now making it nearly 8 years old in a few weeks), that will all keep your system way underperforming no matter if you get a brand new 260 or a old 670 (I am running a 670M).
As the holidays are here deals are easy to be found, your best way to maximize money would be to invest in a i5 desktop computer for only $349 at Walmart, upgrade it with the 650W power supply, and then invest as much as you can afford into any video card you want. You will then have a system that will last you the next 5 years, and be able to play High graphics levels today and the future. BTW that Walmart computer comes with a large HDD, 6-8GB of DDR3 Ram, new keyboard mouse and sometimes a free LCD in the box.