If you're trying to multicam DSLR footage with that setup, what you're seeing is probably to be expected. The bitrate of the DSLR footage is relatively low, but the processing requirements are insanely high--trying to playback three streams simultaneously is just tripling the damage. And, if I'm reading your post correctly, you've already applied an effect while you're trying to multicam--bad news. Do your edit first, and then add the effects later--not only are you trying to decode the H.264 DSLR footage, but you're also trying to process an effect on one or more of the clips. Frankly, I'm surprised your iMac hasn't melted
So, here's what I'd suggest: it flies in the face of the native editing Premiere Pro provides, but I think you'll get better results if you transcode your files to something easier to edit. ProRes, which you're already accustomed to working with, is probably your best bet. Just load up your clips in Adobe Media Encoder (AME), pick QuickTime as your Format, and then create a ProRes preset that is similar to your DSLR clips' properties. I'll assume you have FCP installed, so that you have access to ProRes already. Make sure that when you transcode your files, you use the same file names as the source, but transcode to a different location.
With the transcode files, do your edit; since it sounds like you're already in progress, you can simply make your DSLR clips offline (right/Cmd-click and select Make Offline) and then use the Link Media command to connect those to the ProRes transcodes. Since the file names and extensions are the same--and presumably, the parameters are the same--you'll replace the DSLR clips with the easier-to-edit ProRes proxies. Do your multicam and effects with those. When you're ready to do your final export, you can either use the ProRes files, or repeat the offline/relink process, but this time, link back to the DSLR clips. That way, you're going right back to the "pristine" DSLR source.
Hope that makes sense. I think it's your best hope with the current hardware setup you have. By the way, CS5.5 lets you multicam up to four clips in a single sequence; you can theoretically go more by nesting one multicam edit into another, but you can practically only edit four angles at once.
By the way, what do you mean by:
Does Premier do processing while left alone overnight or is it constantly processing in the background when fed Canon H.264 footage,,rather like FCP X?
Premiere Pro edits all formats it supports natively. Import and edit; that's all. Here's an article by somebody I know about that very thing: Native Format Editing in Adobe Premiere Pro
Hi:Thanks for your quick response.....no, I was doing the color correcting after the multi clip editing....My IMac is fine...in any case I have Apple Care
I don't quite follow the work flow for proxes and such. Have you used Magic Bullet Grinder, the new one? It does Pro Res Proxies but I am not sure how to use it in proxy mode and can't find any video tuts on how to use it with Premier or even FCP
I posted my questions because I was throwing everything I could at Premier and wanted to see how far it can be pushed:)
Does Premier have a better way of reconstituting the Cinestyle flat preset ACCURATELY?