vsync dosent effect performance for christs sake ppl it just syncs the monitor with the card, nothing else sometimes it causes input lag or mouse lag, but otherwise theres no big issue,
40fps with vsync is 40 without it dosent matter, anything over 60 can in FPS games make things smoother but as people well know 300fps is great but some games get fucked up at high frame rates its a balancing act, and i for one prefer image quality, so vsync on in all games but Bad Company 2 when you play games like Oblivion, Fallout 3 or New Vegas, and many other titles, the tearing can be so horrendous it makes you eyes bleed that image posted above, imagine every time you move look around take an action attack somethinge verything that moves the camera causes tearing its insane, certain games benefit from no vsync for sure but most youll never ever notice the difference, in terms of performance anyway.
it really depends on game engine and the game
Dead Space, has mouse lag in menus with vsync etc but as mentioned before, Oblivion tears and has issues with the gamebryo engine. but yea really depends on the title.