My system is anything but slow but Photo Info is slow!
I've used a little application Called PixVue for a couple of years. It integrates with Windows Explorer and is lightning fast. It shows far more image exif data and, yes, you can edit any IPTC fields.
Much prefer it over Microsoft's effort except I've never had a camera that shoots raw so I don't know how PixVue handles it, if at all. I'll find out when my D100 arrives tomorrow.
If you'd like to try it here's the link:
PixVue
I'm not affiliated with them at all, I just use it and love it.