ArtRage 4.5.1 (64bit) has been working great, for me. I haven't had any crashes or failures of any sort. Of course, results will always vary for different computers. I'm on a 4 Core Intel(R) i7-4820k @ 3.70GHz with 12GB Ram, using Windows 8.1 (64bit).
As for new features that you may be worried about missing out on (aside from the speed increase from being 64bit), I hadn't realized how beneficial being able to move the sample colors and presets around the menus would be, but that feature has come in really handy so far. The new font picker has also been nice to have, since it now shows you what the font looks like and makes scrolling through the list of fonts, much easier. I've found the ability to move my presets around between groups, from withing ArtRage, handy. The grid system has been useful for quick centering and alignments (especially when setting up sticker sheets), but I haven't really tried to use it with the Reference system yet, so I can't really comment on that aspect of it's use.
Nothing is easy to the unwilling.