1440×900 . Wil this be the biggest card the cpu can handle
Well, it can "handle" any GPU. But past a GTX 750 TI you won't start to notice as much, as the Core 2 Quad will hit its limit first. The strongest I'd recommend, already into diminishing returns, would be a GTX 760. But a GTX 750 TI would most likely be a better balance of cost/performance on that CPU.