It depends on what hardware you have, what game you're running, and what settings are enabled. Otherwise things wouldn't have changed much at all over the years, now would they have? but since hardware gets radically changed, as do game engines, this varies, so it's impossible to say flat-out where your bottleneck is from the resolution alone.
As far as the aspect ratio goes, 1440x900 is a 16:10 widescreen format, and just shy of 1.3 megapixels in size.