Thanks bulldog.
Personally, I love the Dinan tune. It doesn't cure the off-the-line lag, at least in standard drive, but there's a noticeable improvement over stock in the midrange. I know there are more powerful tunes out there, but since I'm not that experienced with modifying my car, I'm ok with something more conservative with a warranty. Plus Dinan is located in my city, so I had to support the local business.
Anyway, given the weight of the X6 I'd definitely recommend a tune for the 35i, whether factory, Dinan or other aftermarket. Turns a competent but somewhat pokey car into something surprisingly fast and agile.
On a side note, I saw your avatar- you a rugby player? I played in college, rotated between lock and prop. Hence the need for a car easy on my back.
