For 1600x900 - DEFINATELY get the GTX 460. GTX 480 is far more than you need.
And I think you seriously want to look at i7 860 CPU and P55 ASUS P7P55D-E Pro motherboard with 4GB RAM.
If you ever upgrade your monitor to 1920x1080 resolution you could always get a future 2nd GTX 460 - or a next generation GTX 5xx.
You actually bought a i7-930 system with 4GB of RAM?
It has a faster Turbo Core option. i7-930 2.8Ghz Max Turbo Frequency 3.06Ghz. i7-860 2.8Ghz Max Turbo Frequency 3.46Ghz.
In gaming they are virtually identical with the i7-860 being slightly faster in some games because of the higher turbo boost.
You could have spent a lot less and got a system 'just as good'.
If you plan to OC, SLI, or add extra components be sure your power supply will be enough for what you need. To get a good estimate for your current build + plan for future upgrades, visit http://www.extreme.outervision.com/psucalculatorlite.js... and input all relevant fields. (Make sure to include the OC voltage you plan to use) It's always better to have extra power than minimal, especially for OC & future upgradability.