I'm new to the Abarth scene (2 weeks of owning a new 595 Esseesse!) but I would highly recommend calling Paul at RS Tuning in Leeds. For 5 years I ran a Mk3 RS megane that Paul mapped to 300bhp / 350lbs without a single issue. He takes the time to ensure that every parameter of the engine is optimal and always gives good solid advice. It might be a bit of a drive for you but for me I wouldn't go anywhere else.
Now I just need to wait 3 years for the warranty to run out out on the Esseesse before making the trip to Leeds myself. I'm not sure that I can or will though!