+1 @Chino
You only need to upflash firmware when it enables/increases hardware performance, or it enables/increases hardware compatibility (with parts you actually use), or it fixes problems/bugs (which actually affect you). Not upgrading BIOS on a stable system is good advice, you never know when a new BIOS will introduce new bugs or impose limits or break something that works fine on an old BIOS.
ASUS has the unfortunate habit of being (intentionally) vague and cryptic with their BIOS documentation: "Improves stability" or "Improves performance" are often all they'll offer, so it's typically prudent to just install their latest BIOS if you want maximum stability and performance, lol. Many people seek advice on the ROG Forums because their system is somehow unstable or has disappointing performance/overclocks, and they're routinely advised (even by Chino) to "update to latest BIOS" before doing anything else.
BIOS 0503 (G20CIAS0503.zip) is currently the latest-and-greatest version. Newer version(s) could appear any time.
ASUS G20CI Support/Driver & Tools is the one and only OEM source for official BIOS/firmware releases - anything else downloaded from anywhere else is not formally supported by ASUS, not guaranteed by ASUS, and may in fact void your ASUS warranty. Modded firmware can deliberately or inadvertently damage your motherboard/processor hardware, it can even compromise your platform with payloads (rootkits, trojans, loggers, malware) or bugs (increased security vulnerabilities) which run on "bare metal" (ie, executes code directly on logic hardware, "under" all software and drivers and operating systems).
From what I've seen, ASUS *always* changes the version number on every new BIOS (and, these days, also identifies it as Beta when applicable), even if a new BIOS is a "rework of the old BIOS".
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[/Korth]