Benchmarks: PiFast, Cinebench and PCMark
Our Intel Core i5 2500K processor swiftly calculates Pi to 10m places, and the choice of RAM makes little difference to the results.
The same could be said for Cinebench. The intense CPU benchmark uses the Core i5 chip's processing power to render a 3D scene with over 300,000 polygons, but there's literally nothing to separate memory running at 1,600MHz or 2,133MHz.
PCMark paints a more interesting picture. Designed to measure system performance when handling digital photos and video, this benchmark benefits from the added capacity of an 8GB memory kit. There's not a lot in it, but the 8GB kits do begin to pull ahead in the video transcoding benchmark.