Is there a preferred EC2 class when using tsi1?

I know the documentation states using r4 class has shown the best performance, but recently during a demo we spiked with 93% cpu utilization on an r4.8xlarge instance with 3%-5% memory utilization. We have our index version set to tsi1 instead of inmem.

I was thinking of switching to a c5 class instance type. Does anyone have experience with this configuration or suggestions?