The open cars also were allowed to run wider wheels and tires, and had a BOP advantage over the GTP cars until Audi Sport developed the '03 Bentley Speed 8, though it went up mostly against the semi-factory R8s.
It should also be noted that the 500 series cars were initially fitted with 2000 spec bodywork until the '01 LM test day.
Also, I'm curious about the shift points on the R8. Initially the started of with a shift pattern similar to the 2011-2013 R18s (aside from not using 1st gear), then they went to a quicker shift pattern in 2003. I asked about this in the technology thread, but it seems that's not a very well frequented area.
Road America 2002:
https://www.youtube.com/watch?v=PFkQRqmxgZs&t=2869s
Same track in 2003:
https://www.youtube.com/watch?v=AD1BoNqodak&t=4284s
Oddly, the Champion R8 it seems often ran the quicker shift pattern as early as Sebring in 2001. Only big change in the R8's life in the ALMS was a 10% smaller air restrictor that the ACO fitted to all cars after 2002. Was it team preference that dictated the shift patterns? IMO, that's a bit odd given how much Audi Sport micromanaged the privateer R8s.