How do I maximize nvme raid0(md) performance (in linux)?

Michael Hampton and Stuka are right: use fio for benchmarking. Example:

sudo fio --filename=/dev/md0 --direct=1 --rw=read --bs=64k --ioengine=libaio --iodepth=64 --runtime=120 --numjobs=4 --time_based --group_reporting --name=seq_read