Apple created Safari because MS IE 5 was too slow. (I actually like IE 5, but the speed was irritating.)
However, part of what you're talking about is related to the way Mac OS X handles windows resizing.
I don't know the details, but the difference is that Mac OS X does not tear when redrawing, and what this means is you need video cards with insane levels of bandwidth in order to compensate. ie. It works better on recent gaming cards than it does on a Geforce4 MX. I suspect it will be the same with Longhorn - you're gonna need fast 3D cards just for 2D work.
But with Panther X.3 and Safari, I think you'd be much happier.