2500K Turbo Boost works like this:
1 core loaded: 3.7GHz
2 cores loaded: 3.6GHz
3 cores loaded: 3.5GHz
4 cores loaded: 3.4GHz
To test out your Turbo Boost, you have to use a program that can test different numbers of cores. Nova Bench does not appear to have that capability -- it likely uses all of the cores. If you use Prime95 you can tell it to run with one or two or three or four (or more, if your CPU has more cores) threads to test out the Turbo Boost speeds at each load level.