is the gtx 650 ti enough for 1600x900?
Yes. However, I recommend that you get a gtx 660 (Non-Ti) instead if you prefer nVidia.
As regard of drivers, AMD's driver is not as good as that of nVidia but OK under windows. Though, for Linux, you will definitely want an nVidia card as AMD's driver under the OS is terrible. However, I have to agree with others that 7850 would be the better choice compared to 650Ti if you mainly (80% +) use windows OS.