[Helmut Kobler] "I've noticed that the timeline gets laggy when my projects get to 3-5 minutes,"
Keep an eye on your file size for the CurrentVersion.fcpproject file. I found that there are some practices that can balloon your project size, and slow down the application.
I'm working on a 4 minute video now, the timeline index shows 185 items in it, including a bunch of compound clips. There are effects, transitions, lower thirds and other text effects, many connected clips and secondary story lines. The project file is about 25mb, and things are still snappy.
I can point you to the thread if your project seems much larger than that.
As far as using compressor, yes, it's awfuly slow. I've been having better luck using "Export using compressor settings". It sends your project to compressor fairly quickly without actually opening the application. As far as exporting just a portion of a project, I'd be tempted to delete the parts of my timeline I don't want exported, exporting what's left with compressor settings (rendering in the background) then hitting undo to get your timeline back. (Of course before deleting parts of my timeline, I'd make a copy of my project with no renders, just in case the program crashes before I performed my undos. ) This goes much more quickly, and duplicating the project with no renders goes pretty quickly as well.
---------
FCX. She tempts me, abuses me, beats me up, makes me feel worthless, then in the end she comes around, helps me get my work done, gives me hope and I can't stop thinking about her.
Mark Morache
Avid/Xpri/FCP7/FCX
Evening Magazine,Seattle, WA
http://fcpx.wordpress.com 
