You say the full size picture is 1280x800. My monitor is 1280x1024.
I'm also saying that you should make larger sizes, because people have 1600x1200; 1440x900; etc. monitors.
I just made this for personal use, brosef. If you'd like a custom resize, I guess I could try to pull it off. If you have a Mac, you could just make it fill screen or whatever. I'm sure Windows has a similar feature. I use that and have never had problems with pixelation, even with small images.
But this is made with GIMP, a raster editor. How do I make it larger without pixelation?