GPUPI-CLI.exe -d 100M -c ... Calculate 100M on all CPUs in the system and test for the best combination of benchmark parameters (this will take a while)
So probably replacing 100M with 1B will do the same for you ?
Fastest to do is to check the other submissions in the competition... so for me I would try 10M 1024 first to see if it goes a bit faster, but as Jab383 mentions it might not jield the expected result....