Try the free
Faststone Image Viewer. I don't think it's x64 but it's blindingly fast on my x64 rig and totally customizable to one's needs.
For example, I like to be able to use the scroll wheel alone without having to depress any other key to zoom in and out. I was able to easily customize the keys and configure Faststone to work this way. Another cool thing is that it can be set to open image files in full screen with no menus visible (actually I think this is the default behavior, but it's modifiable). But when you move the mouse to either of the top or side edges of the screen, various menus fly out so you can work with your images and as soon as you move the mouse off the menus, they're gone again. It's great if you really want to see and appreciate your images without anything in the way. Plus it has tons of features, most of which I don't need or use because I use other apps for serious PP. It's of the first things I install when I set up a new OS and I make it the default image handling app.