Hey guys, after allowing bigger image sizes in the logo thread, I decided to tweak the guidelines a bit here too. You can use bigger profile portraits if you want, but only if the image still resizes to 300 x 450 when shrunk down. When you're editing it in Photoshop or Paint.NET or whatever, try resizing the image to 300 pixels in width and if it automatically makes the height 450, the image is fine. If it's a pixel or two off, trim the full size image until it can resize correctly. However, if you save a large portrait and the filesize exceeds 1MB you should shrink it down. 600 x 900 is a good size.
If that all sounds too complicated, just stick to 300 x 450. I just wanted to throw the option out there.