Last time I used a 166mhz, the only browser that was usable was MyIE2 Lite. Everything else was unacceptable. I tried Opera, but it was too slow. Some older versions of Opera ran okay, but they were too old and lacked modern features. Some people say K-Meleon is light so that program was installed as a test. The results were not encouraging at all as it took forever to load pages. As you would have expected, even MyIE2 Lite was painful as it choked on pages with Flash which apparently is everywhere. Granted, MyIE2 Lite is just an IE shell, but it had a few extra features and seemed lighter when opening up multiple pages. Its popup blocker also seemed better than just using IE.
Thus in my opinion, a 166mhz system is too slow to be practical today. However, if forced to use a system that old, I would select MyIE2 Lite as a browser.
