Here is a round-up of hands-on reviews and previews of the brand new Canon RF…
Canon EF-S 55-250mm Lenses Spec Comparison
Interesting comparative review of three Canon 55-250mm lenses by dicahub (translated). The EF-S 55-250mm f/4-5.6 IS vs the EF-S 55-250mm f/4-5.6 IS II vs the new EF-S 55-250mm f/4-5.6 IS STM. The comparison is based on specs, never the less it gives a good overview about features. Head over to dicahub for the spec overview.