Netscape 6.2.3 is out. Seems pretty speedy for me but slow startup time and slow when you open a new window. I do think that the best netscape for OS X is still the very first beta version.
That's because Mozilla and NS6 actually follows the W3C recommendations for CSS and DHTML! If you use document.getElementById(), you can make JavaScript code that's valid in both Mozilla/NS6 and IE5+!