WP_MEMORY_LIMIT和WP_MAX_MEMORY_LIMIT的最佳价值是什么？

I have a VPS server with 4 GB RAM and a single WP 4.5.3. The website is really big with many custom tables and large queries.

My current memory configuration is:

php.ini

memory_limit    512M

wpconfig.php

define('WP_MEMORY_LIMIT', '256M');
define('WP_MAX_MEMORY_LIMIT', '512M');

Can I modify any of these settings to increase performance without risking fatal errors during large traffic?

(I also have supercache and cloudflare enabled, my question relates only to memory settings).