A mysterious BMW convertible was caught recently by spy photographers in Munich, with rumors suggesting that this might be a new high-end cabrio aimed at Mercedes’ popular SL-class. Slightly larger than the current Z4, but still down on the SL, the test mule is purported to be the spiritual successor to the Z8 roadster. If this is a new Z9, the car would be sold in both ragtop and coupe body styles and be priced anywhere up to $150,000.

In terms of engine options, BMW already has the V10 from the M5, which would easily provide more than 500hp, or may even consider two specs with a V8 version taken from the current M3, which still produces over 400hp. The Z9 is also expected to use BMW’s own dual clutch transmission technology, which can shift gears in 100 milliseconds.

It was reported that BMW was planning to move the slow selling Z4 up market to accommodate a new entry level Z-car, the small Z2 roadster, so this in could be just the new next Z4. The next generation Z4 is expected to hit the market in 2009 with the new Z9 following in 2010. Follow the jump to see the image in full over at Winding Road.