I have a great collection of underbody pics here: http://www.flickr.com/photos/brgt350/sets/72157634224033500/
Fiesta ST chassis detail 057
by Bryan Redeker BRGT350
, on Flickr
Dave, I put the PumaSpeed/SVT Focus 300mm brakes on my Fiesta and they can't even come close to the stopping power of the ST. Of course, I am running stock pads on my 2011 compared to the ST specific pads on the ST. The OE Fiesta pads started to fade almost right away on track, while the ST pads lasted many sessions with minor fade. The ST booster/master cylinder are also vastly better than the regular Fiesta. The ST acts more like the EU Fiesta in terms of braking, which means it kicks ass. Much like the EU Fiesta brakes, they make a lot of dust. Hawk HP+ kind of dust.
I am not sure of this, but the transmission mount seems to have much stiffer rubber bushings than the stock Fiesta has. I notice very little engine movement on shifts. I upgraded to the Steeda mount on my 2011 and the ST seems to have a mount stiffness that is about halfway between regular Fiesta and the softer option from Steeda. It is stiff, but doesn't shake the car at idle.
One thing I would like different on the ST is more sound from the wastegate when I let off the throttle. It makes more noise on the Fiesta ST than the Focus ST, but could use more. I am afraid of doing intake or exhaust and drowning out what little wastegate sound there is.
What does the Fiesta ST need badly? A shorter shifter with shorter throws.