first of, when you say ram preview, you do mean hitting the zero on the numbers pad, not space bar, right? zero caches to ram and spacebar caches the frames to disk, so space bar may not play back in realtime.
second, if you have a video preview (preferences>video preview) set to play back on an external device (like a deckilnk or aja card, or even firewire) then you can get slower than realtime playback depending on the native settings of the hardware and the comp settings. try disabling the preview to any other source except the computer monitor… if that helps, you may be able to find comp settings that will work better with you device, or try setting the output quality to ‘faster’ in the video preview settings.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW