WHM resource allocation for high-traffic cPanel accounts?

so we've been fine-tuning our cPanel server, really pushing for better server optimization on those high-traffic accounts. getting whm's resource allocation just right, like lve settings, i/o limits, and cpu usage, is proving to be a real beast. its tough to prevent resource starvation or over-provisioning without causing other instability, trying to find that sweet spot. help a brother out please...