We've talked about high octane fuel in here before, and so, although this may be considered off-topic by some, there is a precedent!
My C5 2.0 HPi Exclusive has always run better on Shell Optimax than ordinary unleaded, but yesterday I filled up with BP Ultimate. The performance is _much_ better! Don't know what the octane rating is, but I'd recommend it to any HPi drivers out there.
Steve