I'm using a company called
Courtenay Sport
They were recommended by Ford Motorsport when I contacted them for a certified performance specialist (to go with the [should be] certified driver)
They are based in North Walsham in Norfolk.
These Guys are the dogs dangly bits when it comes to making your car go faster
They also did the modifications to my current chariot, the Vectra B 2.0ltr..but I didn't own it then.
I don't think the performance difference is as much as you think between the 2.5V6 and the ST220....although the 3.0 V6 sounds sweeter, it is not as amenable to tuning as the 2.5 as it is the 2.5 that Ford have modified already.
I think the output of the 2.5V6 in road trim is about 210BHP..but without actually looking it up I could be wrong there. I do know that Ford have undertuned the cars for road use. Originally Courtney suggested that perhaps all I needed was the EMS remapped and the airflow and exhaust "tweaked" as that would give me about 35-40 BHP above the on-the-road power output..but I asked what I could get for 6.5K on a brand new car with only delivery mileage, they suggested that for that money I could easily make the car have the power output of a touring car version but it would take a couple of weeks to get the power output teaks to that level and consistant for road use.
Can't wait..the GF is already dreading it, she reckons I'll look like the Chessire Cat for 6 months after I get hold of it..and she could be right too
Regarding cost, I paid as much for the 2.5V6 as an ST220 costs due to all the toys and extras I added to the package, but I got a great deal from a Dutch Importer and saved, in real terms, nearly £5K, that is why I don't mind spending the difference, and a little on top, on making it go a LOT quicker.