The Core i5 is overall better than the Phenom II X4.
Click link below for comparison between the Phenom II X4 955 (945 is not listed as an option) and the i5-2500k. The i5 beats the PII X4 in every single category.
Note: In some tests, the higher the score the better. In others, the lower the score the better.http://www.anandtech.com/bench/Product/88?vs=288