I bought the ProBook some years ago. It was equipped with an Intel Core i3 Sandy Bridge (HD3000), 4GB of RAM and a 320GB HDD.
It did not take long and I replace the HDD with a 1TB WD Black drive.
Some time ago, I upgraded to OS to OS-X 10.10 Yosemite. I did actually not write about this upgrade. It went very smoothly using clover as boot-manager. I can only recommend that route!
This upgrade got me to using the ProBook more often, so, I decided to add another 4GB of RAM.
Lately, I was using RawTherapee and the GIMP a lot. Image processing is really demanding on CPU-power, so, I finally decided to give the ProBook a real upgrade: a new CPU!
My choice fell onto an Intel Core i7-3612QM.
The Core i7-3612QM belongs to the Ivy Bridge generation of Intel CPUs, the most power efficient generation. It seems that the Ivy Bridge i7 has got the same power ratings as the Sandy Bridge i3.
For reason of the observation, that the battery seems to drain quicker, I am not sure about this. However, it also needs to be said that the laptop seems to stay much cooler, with no additional fan activity.
Beyond thermal and power considerations, the Ivy Bridge HD4000, contrary to Sandy Bridge, is genuinely supported by modern versions of OS-X.
All in all, quite some money went into the upgrades. Still I believe that my ProBook was a lot cheaper than a comparable MacBook Pro.