I'm using JPGs and it's really slow. I'm referring to the Preview app instead of Quick Look in the finder. I use Preview because I can go though pictures and seperate quickly those that out of focus from the sharp pics. Quick Look is also slow.
Over half my SSD is free, so it's not space.
I attempted to use the Preview App from Mountain Lion, but Mavericks refused to let it run.
If I boot from my USB drive to 10.8.5 Preview is perfectly fine, even on the HD with Mavericks. I may just have to boot that way to sperate my pictures until a fix is issued or a setting is changed.