iPhoto slide show not finishing for hours

I'm building a slide show in iPhoto of over 700 images and the I'll export it to iDVD. But first when I export it from withing iphoto, to first build it, with the export button at the bottom of the app. It goes thru all the images ( I can see them in the little preview window next to the progression bar) and on the progression bar it shows about 50% finished and a black slide (which I put in at the beginning and end) and the it just sets there moving very slow and takes around 3 hours a that pont to finish completely. I designed my own title side for the beginning but also have a black slide just before it. Takes around 3 hours a that pont to finish. Please help. Also I reaize it going to tak awhile on the images because here is my sizes 5x7 96dpi
Compression H.264
HD 1280x720 16:9
Preserve aspect ratio using letter box if required (don't know what this means)?
Quality: Best