Looking for ways to speed FCPX

I'm using FCPX 10.1.3 on a 2011 iMac 3.4GHz 32GB RAM Radeon 6970M. I've only just upgraded to 10.1.3 from 10.0.8.

I'm editing a music video using a multi cam clip. I have cross dissolves between most edits. Everything has been reasonably quick, until I started adding other effects and grading to the sequence. Some clips have Digital Anarchy Beauty Box applied. I also have an adjustment layer above the sequence to which I've applied a Tiffen DFX ProMist filter, and another adjustment layer above that to which I've applied an Alex 4d Widescreen Matte.

Background rendering is now incredibly slow. Is this just result of the demanding filters I've applied? Or are there any steps I could take to speed things up a bit?

Demanding filters. Any app will eventually bog down when you apply a ton of filtering. I'm wondering if applying the ProMist and Matte to a single adjustment layer would help? At least it would clean up your timeline a bit. Be sure the matte is second in the filters. But yes, lots of filters will simply bog things down eventually. Have some patience.

Thanks - I'm trying to simplify the filtering - I know that beauty box is an extremely demanding filter.

Also looking for general speed maintenance tips.

My clips and libraries etc are all on an external G Drive thunderbolt drive. Should I be looking at optimising that drive in any way? Or optimising the iMac system?

Optimizing is as outdated and horse and buggies to transport freight.

My recommended maintenance routine is:
Nightly; full backups of media and OS drives.
Weekly; repair all drives with Disk Utility
Monthly; repair all drives with Disk Warrior, verify all drives have at least 15% of each ones total capacity left as free space.