Hi tsantee, many many thanks for your post which has now helped me resolve the issue. I now realise that one of my cameras (Fuji 550EXR) exposes at 30fps even though the setting is on PAL. The fps cannot be changed. My Canon 5D Mk2 exposes at 25 fps PAL and this can be changed - no re-encode required in Toast when using this. Regarding the Slideshow issue, this is also resolved. As you said, Aperture is creating NTSC slide shows. The standard settings for 720p for example are fps 30, Width 1152 and Height 720. Experimenting in 'Custom' and changing the settings have produced really good, cleaner results. For info, when producing slideshows in 720p I find fps 25, Width 1280 and Height 720 are best. For full HD the best results are through settings of 25fps , 1920 Width and 1080 Height.
I'm a very happy man - Thank you.