No, there has to be an alternative. Many (most?) people don't have Calibri, so if there is no alternative, the browser will just pick the next font. You might end up displaying in something stupid like Comic Sans if it chooses alphabetically. It's best to stick with fonts that people have.
Because 60Hz is a really slow refresh rate. If you have a CRT monitor, you should be able to bump it up to 72 or 75Hz without problem. That will be much easier on your eyes. If it's an LCD that only supports 60Hz, then, well I guess you just need to spend less time on it.