Basemark® Metal Free is a graphics benchmark for objective performance comparisons of iOS devices supporting Apple Metal. Integrated Power Board service http://powerboard.basemark.com/ enables you to make comparisons with other devices.
There is also a fully featured professional version of Basemark Metal available that allows users to run custom tests by toggling various graphics features on or off. This innovation enables users to measure how specific graphical effects tax the device and to detect performance bottlenecks in a super easy and intuitive way. The professional version will be a boon for every game developer or tech enthusiast who wants to check out how well different phones and tablets support certain graphics features that are commonly used in the mobile games.
More information: http://www.basemark.com/product-catalog/basemark-gpu-mobile/