When looking at the OpenSSL RSA 4096-bit signing performance, the Core i5 2500K had annihilated the Core i7 970. The quad-core Intel Core i5 2500K was 61% faster than the Intel Core i7 970 when both were at their stock speeds.
When looking at the x264 video encoding performance on the Core i5 2500K, its performance fell far short of the Intel Core i7 970 with its greater number of threads. Though the x264 video encoding performance for Sandy Bridge may be improved greatly once Intel releases their modified x264 library to take advantage of the transcoding support. The Intel developers are also working on video encoding acceleration on the Sandy Bridge CPU that would be exposed via VA-API, but it's not here yet, only the video decoding support on Linux is currently ready and available.
Ending out with some server-focused benchmarks, the PostgreSQL database server heavily favored the Core i7 970 and it is three times the number of threads as the i5-2500K. The Core i7 970 performance at stock speeds was 2.33x greater than that of the Sandy Bridge CPU we were testing. When this CPU was overclocked to 4.2GHz, the i7-970 was still 28% faster.