If it has a generic tune I'd say valve springs if the car runs like crap then clears up without a restart. Overboost from memory requires a restart to run properly again afaik. You can remove the spark plugs and squash the gap down to 0.70mm to save screwing around. I always did 0.60mm with 18-20psi on my BA and 0.65mm on my 08 F6X. As for boost, I'd buy a generic obd2 dongle (Bluetooth, wifi or usb) and use the Torque application from the Android store or use ForScan with a laptop (free license for a set amount of days). That will tell you what boost you are actually running as well as some other things like Long and Short term fuel trims etc. If you can I'd jump on the highway in 3rd gear from as low an rpm as possible (needs to be in sports mode with you manually changing the gear so it doesn't jump down a gear) and full throttle if you can up until at least 4500rpm+ (speed issues is more of a concern by this point). Have a mate with you to monitor boost, I assume you've tapped into the vacuum line at the manifold? Other little things are cleaning the throttle body and using a catch can so it doesn't ingest oil from blow by at its age.