Here are few ways which helped me reduce or completely erase the fps drop:
In game methods:
1. Delete all mails
2. Delete all contacts
3. Delete/sell all useless assets
4. Delete all useless channel
5. Delete all troll/useless fits
6: Recue texture and graphic detail to medium/low

External methods:
1. Delete the saved game data utility of the games which you don't play anymore
2. Delete all useless saved files
3. Delete all inactive psn contacts
4. Delete all psn messages
5. Delete useless pictures and video
6. Delete any other game in the memory which you don't play anymore
7. From the setting reduce the graphics from 1080p to 720p hd. (Google it if you have a doubt)

This has helped me a lot. I have not experienced any fps drop.

Bonus: Last resort (Do this at your own risk)
Delete everything from your ps3 that consumes memory. Eg: Youtube, netflix etc
Delete every psn contacts
Delete everything but dust. Let your ps3 solely focus on dust.

Note: This is will get you rid of fps drops but not sever based lag/rubber banding.
How this works?
- Well its quite obvious, by deleting all this you are making a lot of space in the memory and reducing the burden on the RAM. In other words your ps3 will now focus on dust improving your performance.

Hey thanks for the heads up, some of this is elementary but I had not considered to remove things like PSN contacts and such so thanks for that idea.

Just wanted to also say however that DUST natively runs at 720p so turning your hdmi settings down from 1080 to 720 should not actually do anything (should being the optimal word). That being said if you do want a big performance boosts, dropping the setting on the HDMI down to 570ish or what ever that lowest setting is, will increase framerate and reduce input lag. Only problem is you cant see anything because its all chunky pixels lol

Setting the ps3 in 720p won't change anything as it automaticaly do it when you play DUST ^^

I reformated my ps3, rebuilt the database, have 20 contacts left (used to have 100), only have Dust, deleted everything I could delete and still.. I have hard FPS drops..

Delete everything but dust. Let your ps3 solely focus on dust.

But.....the classics!

*GOOD STUFF*

How many load-outs do you currently have?
Have you performed a spring cleaning on your inventory?

Here are few ways which helped me reduce or completely erase the fps drop:
In game methods:
1. Delete all mails G£ô
2. Delete all contacts G£ô
3. Delete/sell all useless assets G£ô
4. Delete all useless channel G£ô
5. Delete all troll/useless fits G£ô
6: Recue texture and graphic detail to medium/low G£ô

External methods:
1. Delete the saved game data utility of the games which you don't play anymore G£ô
2. Delete all useless saved files G£ô
3. Delete all inactive psn contacts G£ô
4. Delete all psn messages G£ô
5. Delete useless pictures and video G£ô
6. Delete any other game in the memory which you don't play anymore G£ô
7. From the setting reduce the graphics from 1080p to 720p hd. (Google it if you have a doubt) G£ô

Delete everything from your ps3 that consumes memory. Eg: Youtube, netflix etc G£ô
Delete every psn contacts G£ô
Delete everything but dust. Let your ps3 solely focus on dust. G£ô

Do the magic anti-Framerate drop dance G£ô