I think you may be comparing single-core turbo against all-core turbo speeds. ark.intel.com doesn't list the 8175M, but all the similar models have 2.1GHz all-core turbo with single-core turbo around 3.7 or 3.8 GHz. Other sources list the 8175M as having a base frequency of 2.5GHz and single-core turbo of 3.5GHz.