No, all the pics on his home page are about that size or less. His Pixiv site has bigger images, but this one isn't among them. If it helps, this is the cover from a CG set he published on CD in 2006 called "夏日斑" (perhaps someone could translate that). It's no longer available.
Aside from the odd wallpaper size pic, his CG set CDs don't have any pics in even half-way decent resolution, they're not even 900 pixels in the tall dimension. I really don't understand why anyone would buy them actually.