Fastest "view only" model for client

I have only a little, simple experience with SU (running v8 free on XP 32bit). I have a VERY LARGE (file size) and detailed model that a client needs to view ASAP. I am already dealing with LAG TIME (in multi-minutes) for most actions I take in editing, saving, etc. but the client must be able to view it much faster, but does NOT need ANY editing capability. I am already taking steps to reduce the file size. but I need some solid advice here.

I need a combination of “file format” with a free viewer (to send with the file) that is as fast as possible. I have several tools for conversion (some work, some don’t). Something that would create a version of the model that has ONLY the visible surfaces for viewing if there is such a thing.

Any Help?