The original JLP Kangaroo version 1.7 gives a speed of about 700 Mk/s for GTX 1660 Super, a few changes in the code and the speed will be 1.1 Gk/s and around 2.2Gk/s for 2080ti.
What grid size are you using with the "original JLP Kangaroo version 1.7" in order to see it at 700 Mk/s on a GTX 1660S? Are you sure about that speed being real?
Cause with no code changes and using the 1.7 release tag, I can't go beyond 300 Mk/s (or rather, ~250 in reality, since stats display is kinda broken) on a card that is both newer and superior to that model. And looking at the nvcc compile stats, I have some doubts that it would even be capable to go at a triple speed, on an inferior card with 25% less CUDA cores.