Should I be able to run ICO at 4x native inside a 1280x960 window?

I've tried it, and it looks a lot nicer than just running at 2x native inside that window, but wallops my frame rate as well -down from 60 to 30ish and below.

System is i5-2500k @ 4Ghz, 8GB RAM, GTX570.

Running the plugin in DX11 mode.

Yes you can run it at any size window, directx will automatically scale it down, though you might not notice much difference from 3x and it might take a speed hit.

But my main question is, why is there such a drop in FPS from 2x/3x to 4x, bearing in mind my PC specs?

To understand it easier imagine Native as 1 square, x2 native doubles width and height soo you have 4 squares, x3 native means 9 squares, x4 will mean 16 squares;]. It's not always soo exact especially that your gpu isn't really used as it was designed to, soo it often reaches different limitations, but that's generally how more demanding it get's. x4 is simply 4 times more demanding than x2;].

The fps is definitely not right for that card... Even my 560m can handle 4x on Ico. This is with latest nvidia drivers and pcsx2 r5178

How are other games playing at 4x?