SSD IOPS suggestion for OSM tile server

I have provisioned an OSM tile server, but rendering is still a little slow (60Gb mem, 8 CPUs). The postgresql data is living on an AWS throughput-optimized HDD, but I am considering trying an AWS SSD with pre-provisioned IOPS to see if that improves rendering. Are there recommendations for IOPS provisioning for the rendering disk? AWS makes you pay for provisioned IOPS, as well as storage. I don't want to over do it, but also don't want a bottleneck.