No issues on smallnetbuilder.com on iPhone 8 Plus or on iPhone 6, although the 6 seems to be loading even though the website is usable. That site is awful on mobile though, and I would assume if you are using a ton of apps those phones with 1GB ram will struggle.
Also quick update, iPhone 6 scored 1550/2600 on GB4 once the battery got to 100%. The battery in this one is pretty awful, it takes a LONG time to charge to 100% so keep that in mind. Pretty snappy though, some frame drops/stutter here and there but overall an improvement from before. I don't use it other than as a backup and for testing, so I can't really comment on battery life.
EDIT: Using Crystal on 8 Plus, no content blocker on iPhone 6