I use DNSBlast and DNS Benchmark to load test my piholes.
My pihole run unbound also.
One thing I have found is the dns cache time increases under sustained heavy load.
I made a video so you can see it in action but there is no sound.
The command is ./dnsblast ip 900000 200
https://github.com/jedisct1/dnsblast
https://www.grc.com/dns/benchmark.htm
I have been using The Yacy Search Engine for the past few months to harvest information.
I have supported since about 2011.
The test crawling was done at a Depths of 40 - 50 in the PIC.
The Yacy version is 1.924/9000 Before the DNS settings where turned down for the home user like me.
I use the Pihole to block sites that slow crawling down or hang Yacy.
Thanks