To achieve 3.1 GHz Turbo Boost - you could only utilize one quarter of your CPU.
This does not nearly compensate performance-wise for a well written program that would utilize all cores. While it's a nice feature, it's usually not a performance boost on top of the stock performance of all cores being completely utilized.
You are mixing things up:
SpeedStep is a trademark for a series of dynamic frequency scaling technologies (codenamed Geyserville and including SpeedStep, SpeedStep II, and SpeedStep III) built into some Intel microprocessors that allow the clock speed of the processor to be dynamically changed (to different P-states) by software.
http://en.wikipedia.org/wiki/Intel_speedstep
Intel Turbo Boost is a technology implemented by Intel in certain versions of their Nehalem- [...] Haswell-based CPUs, including Core i5 and Core i7, that enables the processor to run above its base operating frequency via dynamic control of the CPU's clock rate.
http://en.wikipedia.org/wiki/Intel_Turbo_Boost
All the info in /proc/
and /sys/device/system/cpu/
is always limited to regular frequencies by design; see https://kernel.org/doc/Documentation/cpu-freq/boost.txt
comment by Class Stacker on question Is Turbo Boost Working?
Some CPUs support a functionality to raise the operating frequency of
some cores in a multi-core package if certain conditions apply, mostly
if the whole chip is not fully utilized and below it's intended thermal
budget. The decision about boost disable/enable is made either at hardware
(e.g. x86) or software (e.g ARM).
https://kernel.org/doc/Documentation/cpu-freq/boost.txt
Simply put, your i5 CPU decides for itself if it applies boost or not and Linux by default doesn't care much about providing accurate and detailed information for this.
cpupower frequency-info
.