Ok, on this vise thing. I purchased a 3" vise from LMS thinking maybe it would be better than the Chinese ones on eBay. WRONG! same exact vise, I tightened the jaws up on a piece of aluminum and right out of the box it didn't feel like it was tightening correctly. You know that feeling you get when you expect something to have resistance as it gets tight? well this didn't have that. That's because it was screwed up. There is a set screw that pushes the jaw closed against another radius part, that is supposed to provide the downward force like the Kurt brand, mine was messed up and required fixing (right out of the box). Do a search for polishing a turd and you will find an article about these vises. I ended up fixing mine up enough to use but its hard to trust it.
I'm not knocking LMS they are simply re-sellers of imported goods. My next vise will be a Glacern 4" myself, quality only costs a little more.
As far as size, think about how much of the vise will hang off the front over the Y axis handle, a 5" vise is almost 15" long.
Just food for thought.
Mark