Having spent 15 years in engine tuning albeit mainly petrol with a 4 year stint at MoTeC and another 5 years after that in motorpsort, I revel in the opportunity to get the most of of a standard engine. Sure you can get bulk horsepower with extra strong internals, a larger turbo etc but the former approach is my preference....

However......The X5 ECU like in my 2004 model can only be written to (re-programmed) less than 10 times before it locks up and you need to get another unit from somewhere to replace it. This appears to be deliberate protection by Bosch/Siemens/BMW to limit the number of updates or re-writes.

I have seen ECUs rendered useless by well meaning operators re-flashing ECUs in Subarus, VW's and more. Just make sure that whoever is doing this for you, is prepared to supply or have available another ECU as a back up.

A reflash has many advantages IF the programmer/s are very experienced and know their way around the architecture. As long as they don't use your car as the guinea pig and there is some form of recourse if it all goes pear shaped, then let me know how it goes.

My 5c worth.
Cheers Dan.