This was an interesting comparison of two somewhat older dry Rieslings from the same producer (Kesseler) and vintage (2001). As you can see, I preferred the Roseneck, but tend to usually prefer that site over the Schloßberg, which is a very good vineyard in its own right.
2001 August Kesseler Rüdesheimer Berg Roseneck Riesling Spätlese Trocken
Limestone/petrol/floral/peppery nose. Full, ripe, round, bone dry; well balanced, with good underlying acidity. Quite mineral, with notes of white peaches, red plums, hay, and honey. Needs about an hour or more to really open up. Excellent.
It's worth noting that Kesseler made a Großes Gewächs from Roseneck in 2001 (I'm not sure about Schloßberg?), so this supposedly wasn't his top dry Riesling from that site. It could easily have passed for GG quality in my book - I've had a lot of less compelling GGs.
2001 August Kesseler Rüdesheimer Berg Schloßberg Riesling Spätlese Trocken
Toasted corn/lightly mineral/stone fruit nose. Full, round, juicier, softer, bone dry, well balanced, with moderate acidity; not as structured as the Roseneck, but more approachable. Moderately mineral, with notes of apples, apricots, plums, white pepper, hay, and chalk. Somewhat dusty multigrain note on the finish. Very good/excellent.
Finally, I don't understand why, but I have not found many post-2004 wines from Kesseler in the Boston area, aside from the basic estate Riesling (mediocre in my opinion, even for the QPR), and the entry-level Pinot Noir (a solid wine). This is strange given that they are distributed by Vineyard Brands, which is quite active in Massachusetts.