I set my project settings to HD 1080-60i (1920×1080, 29.970 fps) Field order = Progressive, quality = best, deintetlace method = none for slide show HD videos. Just placing them back to back on the timeline, my dual core 3.4 laptop works great with preview set to best / full. Are you using alot of effects? What do you mean gettin slow when project settings are HD, HDV AVCHD. There is no AVCHD project setting. If your talking about rendering that’s different.