That's a excellent low weight for a RS4 S8
I'm jealous, I estimate my S8 (also manual) is at 1749kg with full tank but me not in the car!
I bet you saved a lot of weight with racing front seats, just out of curiosity do you know the weight of your racing seats?
I know the S8 standard Recaros weigh 34kg each which is a lot.
Also I think the rear seats weigh 30kg so that's a lot you saved there too.
Impressive!