Unigine Heaven 4.0
“Heaven Benchmark with its current version 4.0 is a GPU-intensive benchmark that hammers graphics cards to the limits. This powerful tool can be effectively used to determine the stability of a GPU under extremely stressful conditions, as well as check the cooling system’s potential under maximum heat output. It provides completely unbiased results and generates true in-game rendering workloads across all platforms, such as Windows, Linux and Mac OS X.” From Unigine.com.
at £125, it takes it into 7850 1gb territory, I concur with your conclusion, its certainly overpriced, and limited by that 128 bit bus width, for the same money you could get the 256 bit 7850 1gb, the memory throughput is so much better, and will allow the VRAM to be overclocked, SCAN has an MSI 7850 1gb for just £123.34, making this 2gb 7790 variant redundant.
http://www.scan.co.uk/products/1gb-msi-radeon-hd-7850-4800mhz-gddr5-28nm-gpu-860mhz-1024-cores-hdmi-2x-mdp-dl-dvi-i