Noticeably more aggressive from the moment you press the Collins Performance-branded starter button and fire it into life. Our car's burbling single-box exhaust can be swapped for a quieter twin-box item for no extra cost, but if standing out is your thing, we'd keep things as they are here.
Pulling away reveals two things. Firstly, CP hasn't messed with the gearbox, which is a very good thing: it's as slick and positive as ever. Secondly, and less appealing, is the amount of vibration sent through the cabin by the exhaust as the car pulls itself out of low revs.
Around town, it's a matter of persevering with them, but once the road opens you'll likely forget them. Flooring the throttle is followed by a second or two of the new turbo whistling to life before the front wheels and traction control begin some serious negotiation.
However, the visions of a tyre-smoking, torque-steering, leafy accident - in that order - never become reality. In gear, power and torque delivery is progressive enough to ensure that traction eventually wins the day, the steering wheel doesn't squirm uncontrollably in your hands and performance is hold-on-tight impressive.
Some of the figures we experienced tell the story. Our CP Fiesta was 1.4sec quicker from 30-50mph and 1.8sec quicker 50-70mph in fifth gear than the standard ST, and with its traction control switched off (and some careful clutch control) we managed to fire it from 0-60mph in 5.9sec - a second quicker than standard. An entry-level Porsche Boxster is just a tenth quicker.
Of course, just like the standard ST, stamping on the power too early mid-corner causes the front wheels to run wide, only more dramatically so. But this is just as easily remedied by lifting off, listening the turbocharger exhale with a hiss, feeling the back wheels inch out and tucking the front wheels back on course.
Collins Performance found that the CP3 pack made the ST's standard chassis snappier at the rear than usual, but if anything, we think the front end has lost just a hint of its urgency with the Dynamic Chassis upgrade's stiffer bushes.
We're talking minute differences, though, and without trying both back-to-back it's hard to judge whether spending the extra on it is necessary. Ultimately, it'll make little difference on the road, and even if you were slightly slower cornering on track, you'll be having just as much fun, and more than make up the for lost split seconds by barrelling down the straights more quickly.
The CP3 pack can be fitted to any grade of ST, but our car was an ST3 model, so came with everything the standard car does - most notably the superbly supportive Recaro front seats and sat-nav. The branded starter button, boot lid sticker and engine cover branding are standard, but thankfully the side stripes and exterior branding aren't - they're another £120.