For fast viewing of high res digital image files I use ACDSee Pro 10. Without it, large images can lock up computers not designed for photography. Also, without it, images can be cumbersome slow for image viewing.
Pro 10 retails for $100, and regularly on sale for a 50% discount. The only difference in Pro and Standard ($60 retail, $30 on sale), Pro allows embedding metadata within the file, such as keywords, captions, etc. If you don't use metadata, Standard works just as well. ACDSee offers a 30 day free trial from their website. I paid $50 for Pro 10. For Mac users ACDSee makes a Mac version here.
Go to the ACDSee Website here.
I am not paid in any way for this recommendation. Just one of the products I use in my workflow process.