At the risk of opening fresh wounds...
There's really no need to do anything to reduce the weight on your bike. The influence of weight on performance is vastly overstated; and it's already 20 pounds, which is very light for a folder. If it's genuinely faster than the Speed (rather than just
feels faster -- a very common, and inaccurate, impression when you get a new bike
), it's almost certainly due to better aerodynamics and the lack of suspension.
If you've got the Need for Speed, I'd look into different tires -- something slick, narrow and with a high PSI. I found the Schwalbe Marathons to be robust but kind of pokey, especially on turns. Good for commuting but not particularly fast.
Al Q: Gearing has some impact, but not much. The biggest
mechanical impediment will be the position; looks like the Mu SL does not have an adjustable height handle post, so if the bike puts you in an upright position, you're.... kinda screwed. Sitting upright, you'll have far more drag than a roadie whose handlebars are 3" below his saddle.
For the creaking: Check all the hinges thoroughly, make sure they're adjusted properly, and grease the seat post.