Yes, LW 5 does not behave super well with when you are using the old LW 4 preferences. Issues that may affect it are: lots of incomplete files & lots of shared files.

Try deleting your LW preferences folder whilst LW is closed (must be closed!) Description of how to do this here: Deleting LW Preferences folder in OSX However, I do highly recommend you make a note of all your settings before you do this. Next time you open LW you will be asked to do new settings which includes download location, shared folders, etc. So take it slowly & carefully.

Try to get rid of some of the old incomplete files. You will need to cancel them from the downloads first. Then remove from the incomplete folder. Get rid of the older ones first. You can arrange your incomplete folder via date. Tip: Purge the Downloads Queue! (click on blue link). Instructions shown here are for LW 4 however same principle applies. Quick access to Downloads window is via menu bar, Tools > Downloads. I haven't tried, but you might be able to Control or Command click the incomplete files from the Download window & choose remove or delete. I need to check up on that sometime. Edit: Just checked, you have a Cancel Download option only after Control clicking the incomplete file in the Download window.

BTW I had freezing problems too whilst i was running the earlier LW 5 alpha version. One reason was so many images to load, another was loading so many music files into my library. I reduced my shares down a little, especially for images.