[quick6]

I just tuned my M6 and thought about it long and hard. I chose to go with a more moderate tune from VF Engineering, stage 1 with 612 whp or about 720hp at the crank. Its plenty fast and I'm not worried about the motor blowing up.
Just let it warm up before redlining-don't beat on the car and you should be fine.

The law says that any failure must be traceable to an aftermarket tune or part. For example, if your fuel pump goes or rod bearings, they'd be hard pressed to prove a tune was directly responsible for the failure. There is some risk, without a doubt and I also have an aftermarket warranty. The VF tune also lets one put it back to stock before visiting a dealer for service but if you are truly anxious, don't tune the car.
Its a risk, but not huge as there are thousands of BMWs running around with tunes.

P.S check out some of the responses to "High Mileage M6's check in" post and there are a lot of older, M6's with high mileage and tunes.