I use my Cossie a fair bit around town and it was returning a cracking 8mpg

This was mainly due to the grey injectors and crappy map from a shitty local tuner (I bought the car like this) as I know it was running far too rich.
Ive now bought a set of Siemens black injectors, and was planning on going Stu's closed loop conversion to improve MPG, but would I be better off getting a live map to improve both MPG and drivability? AS Ive heard Stu can get very decent Co levels without closed loop.

What is best suggested?

Also find the car a bit laggy (well technically boost threshold) when coming on boost, its currently on standard head and cams on a T34.63. Would changing a cam make it any better?

Cheers