to tell if your CPU is bottlenecking, install a GPU monitoring program like MSI afternburner. go to the options and make sure that the GPU load percentage is OSD (on screen display). if your GPU load is around 90-100%, your CPU isn't bottlenecking. if it frequently drops below 90%, your CPU is bottlenecking your GPU. but my guess is that it is, because my pentium D 3.2GHz scores about 900 points in CPUbenchmark and bottlenecks my GT520 by a lot, depending on how CPU intensive the game is. in team fortress 2, my GPU is at about 5-10% load, which means my CPU is bottlenecking it by 90-95% of it's full performance. (i get 1-5 FPS ) your CPU scores only 300 more points than my pentium D, (887 points vs 1245) and you have a better GPU. i'm guessing that your CPU is bottlenecking by 30%, but again it depends on the game you are playing. i would do a full system upgrade. it's pretty old. very soon your CPU won't be able to do any gaming above 30FPS. i'm surprised you are still using it.
vsync won't help at all. all it does is lower your FPS. say your monitor is 60Hz, that means it can only show a max of 60FPS. if your GPU is outputting more than 60FPS, if look look left and right you will notice vertical tearing. ( http://www.nhancer.com/help/images/VSync.png ) the top half of your monitor will be ahead of the bottom half of your monitor. the top half is a frame ahead of the bottom half. to fix this problem with people who have high end cards and get over 60FPS in games, they enable Vsync which makes it so your GPU doesn't output more than your monitors refresh rate so there is no vertical tearing. if you get under 60, it goes directly down to 30. so if you were getting 50FPS, vsync will only allow you to have 30.
Nvidia made this new technology called adaptive vsync. this means that when you fall below 60FPS, vsync will automaticly be turned off, so you can actually get that 50FPS instead of being locked at 30 and 60. and when you hit 60 again, it turns back on automatically. this technology is only supported by Nvidias 600 series.