Are you thinking of the i5 750/760 or the i5 2500k/2500/2400?
i5 750/760: This only has 4 cores and 4 Channels with a frequency of 2.66/2.8Ghz. The i7 950 has 4 cores but 8 channels, meaning that that the processor will be able to handle information more efficiently and process it at a faster rate. It also runs at a frequency of 3.06Ghz. The i7 950's motherboard would also let it handle more modules of RAM (6 vs 4).
i7 950<i5 750/760
i5 2500K/2500/2400: Intel's new line of processors. Has 4 cores and 4 channels but a very different architecture that makes it equal to the i7 950. It has a different motherboard to the i5 750/760. It also has an integrated graphics processor, which is not as powerful as a discrete but is more powerful than the previous line of Intel graphics. Also only has 4 RAM modules.