So, lately a new GPUs benchmarks and info system has been published on this site. The available data is accessible via the GPUs list page along some rough performance score and some very basic data. Moreover, it is now possible to compare GPUs at the gaming level. It is accessible via this page, which allows choosing two GPUs to compare. When comparison data available, it usually includes multiple gaming benchmarks for various resolutions.
GPU comparison is mostly for games, but adding syntethic benchmarks (3DMark, TimeSpy, etc.) is underway. Please check it.