Your project is far too long for easy editing in FCP X.
Break it into sub-projects (chapters if you like) of no more than 20 mins each, then when every section is complete, make a Compound Clip of each sub-project and add them all into a master. Just a few more tweaks, and you can export (sorry - share) from there.
Also, make sure all your Events and Projects are on fast external hard drives - trying to work with them on the system drive will cause serious slowing down.
Additionally, how complex is your project?
I sometimes do projects of 2+ hours with no problems whatever, but they are comparatively simple . . . . mainly a single timeline and 3 audio tracks with titles, credits, cuts, cross-dissolves and the occasional effect or generator.
If yours is composed of multiple video and audio tracks coupled with numerous effects you may well experience problems especially if you are using one hard drive and it is more thn 80% full.
Another thing that may cause a slowdown is having too many projects and events.
Any that you are not using should be "hidden" by moving to separate folders.
I have all the events file on one dedicated 3T drive 7200. It has 956 gigs free, so roughly 2/3 full. My project is a series of interviews with modern and archival footage. Some of the archival footage is standard def but most all is HD. Sometimes there is just one soundtrack and sometimes there are as many as six or seven depending on the media. The additional tracks are mostly sound effects and narration. I do put effects on some of the archival footage to sharpen it and give it it's color back.
I may try breaking it up as andynick suggested. Need to do something because currently it has become a nightmare.
This is my pet checklist for questions regarding FCP X performance - you've clearly addressed some of the items already, but it's worth checking.
Make sure you're using the latest version of the application - FCP X 10.0.5 runs very well on my 2009 MacPro 2 x 2.26 GHz Quad-Core Intel Xeon with 16 GB RAM and ATI Radeon HD 5870 1024 MB. I run it with Lion 10.7.5.
First, check that you have at least 20% free space on your system drive
If you have not already done so, move your Projects and Events to a fast (Firewire 800 or faster) external HD. Make sure the drive's formatted OS Extended (journalling's not required for video). You should always keep at least 20% free space on the Hard Drives that your Media, Projects and Events are on.
Check the spec of your Mac against the system requirements:
Check the spec of your graphics card. If it's listed here, it's not suitable:
If you are getting crashes, there is some conflict on the OS. Create a new (admin) user account on your system and use FCP X from there - if it runs a lot better, there's a conflict and a clean install would be recommended.
Keep projects to 20 mins or less. If you have a long project, work on 20 min sections then paste these into a final project for export.
If you ever experience dropped frames, I strongly recommend you use ProRes 422 Proxy - it edits and plays back like silk because the files are small but lightly compressed (not much packing and unpacking to do) - but remember to select 'Original or Optimised Media' (FCP X Preferences > Playback) just before you export your movie, otherwise it will be exported at low resolution.
If you have plenty of processor power, for the ultimate editing experience, create Optimised Media - most camera native files are highly compressed and need a great deal of processor power to play back - particularly if you add titles, filters or effects. ProRes 422 takes up much more hard drive space but is very lightly compressed. It edits and plays back superbly.
Hide Audio Waveforms at all times when you don't need them (both in Browser and Storyline / Timeline). They take up a lot of processor power. (Use the switch icon at the bottom-right of your timeline to select a format without waveforms if you don't need them at the moment, then switch back when you do).
Create folders in the Project and Events libraries and put any projects you are not working on currently, in those folders. This will help a lot. There's a great application for this, called Event Manager X - for the tiny cost it's an invaluable application.
Unless you cannot edit and playback without it, turn off Background Rendering in Preferences (under Playback) - this will help general performance and you can always render when you need to by selecting the clip (or clips) and pressing Ctrl+R.
The biggest single improvement I saw in performance was when I upgraded the RAM from 8 GB to 16.
It may be nothing to do with it but it is always worth trashing the prefs with http://www.digitalrebellion.com/prefman/
On several occasions during the past 7 years I have cured problems with legacy FCP and FCP X by eventually trashing the prefs, after struggling for hours or days, because I believed at the time that the trouble was nothing to do with them.
So now it's something I do immediately, if only to rule it out.
Most likely the problem is starting a project in one version and then updating bfore you have finsished which is never a great idea.
I am getting spinning beachballs with a previous project where I did the same as you against my own advice.
80 minutes should not be a problem assuming yu have plenty of RAM?
There already is an App called Preference Manager by the way