Sorry late to comment - and also been off line for months - sheer pressure of work
Like you I'm in God's own County- and did much the same journey down for map work. I've mentioned it multiple times - I'd always been uninterested in mapping a car- as had heard and seen many horror stories.
The reality with Leighton was- he was mindful of not hurting the car. And carefully configured mine (standard model no upgrades added apart from OEM+ parts to replace old). The before and after attects were really impressive. Mine made circa 266 bhp. Likely a next model up turbo would produce higher figures- but at the same time I got better MPG and just oddles of torque everwhere off boost.
Hope to see you car someone where around the City at some point!