I'd personally recommend Redline SI-1. Use a full bottle with a full tank the first time. Then do the 'maintenance dosage' the rest of the time.

I've tried Chevron Techron, 3M Complete Fuel System Cleaner, Berryman's Complete Fuel System Cleaner and Redline SI-1. To be honest, I ran through them all within 4000 miles. I was troubleshooting a fuel delivery problem. Anyway, even with using them so close together (which can be dangerous to the health of your valves and injectors), the Redline I used last and even though the other 3 preceeded it, I still noticed a slight increase in performance and responsiveness. It's more snappy now. Flooring it to redline is also alot more responsive. Seems like once it hits 5K - it just pulls really hard. Granted it may be compounded by the use of all 4, the Redline made a difference even though I used 3 before that.

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2006 X5 3.0L - Schwarz Black/Truffle Brown
Stock
But I keep it clean