Looking to run a Roku Ultra to an AVR then about 20 feet to a Benq projector. Thinking fiber optic HDMI because of length, but question is do I need an HDMI that's 48 gbps, or is 18 good enough? Thanks!
No way to know unless/until you go - there have been reports in the past from users that had very long HDMI or fiber optic runs that had EDID/handshaking issues, especially when their firmware upgraded.
18 *should* be good enough, but perhaps 48 will cover any future upgrades of devices in the run/chain.