Question : Problem: Confirming replacement of defective parts with lower rated parts than original?

How do I go about CONFIRMING that a LESSER motherboard was installed in my laptop when I had the motherboard replaced a few months ago?

Approx.  1/05 I purchased a 1.7 GHZ laptop and was pleased with its performance.   Then in 2/06 the motherboard failed due to overheating.   I had a PREMIUM service contract,  I had no problem getting the local computer store (where I originally bought the laptop) to replace the motherboard.
But ever since it came back,   I sensed that it wasn't performing at the level that it had when the laptop was brand new.    I had more pressing problems in my life so I didn't persue the matter until a week ago when a software conflict arose,  and I had to take my laptop back to the dealer for software reconfiguration.      During the 2 days my laptop was in the shop,  I relied on an old 700 MHZ desktop  workstation on our office network.     And when I went to pickup my laptop,   I make the comment that that old 700 MHZ machine seemed to be faster than my 1.7 GHZ laptop.    The response I  got was most likely my laptop had some kind of malware and/or virus.

But I have attempted to maintain the highest degree of proper protection against malware and viruses,   through the use of Symantec software,   Ad-Aware,  etc.

Then last night I was browsing a user forum for the brand of my laptop,  and came across a posting by an individual who had sent his 1.7 GHZ computer in for motherboard replacement,  but the repair shop had failed to properly reinstall the motherboard,  such that it was not running at the 1.7 GHZ speed.   In his posting,  he stated that he had used Belarc Advisor to diagnose the specifics of his computer,  which confirmed that he indeed had a 1.7 GHZ mother board,  but which was not running up to its potential.    

So then I downloaded Belarc Advisor,  and ran it on my laptop.   To my horror,  it came back with the report that motherboard currently in my laptop is 600mhz,  and not the 1.7 GHZ that it has been represented to me.    
How likely is it that the computer dealer relied upon his supply source for replacement parts,  with the possibility that the supply source (manufacturer or some middle-man parts source) is the true guilty party who switched out a 1.7 GHZ motherboard for a 600 MHZ motherboard? (which the local repair shop never noticed)?

The local computer dealer HAS BEEN a personal friend of my partner and I,  so I need to proceed carefully before any "bridges are burned".  

How do I go about CONFIRMING this in a manner that will give me an airtight case so that I can nail this computer dealer to the wall?    

What is the chance that this Belarc Advisor might be providing me with a mis-read?

Answer : Problem: Confirming replacement of defective parts with lower rated parts than original?

First we need the details of the laptop itself, brand- model # .
When you used Belarc were you running on battery or directly from the AC adapter. Some laptops will clock down the CPU when on battery in order to save power.
There is a simple program that will give you alot of info about the CPU motherboard and ram called CPUz.
Try it and see what it says about your CPU.
http://www.cpuid.com/download/cpu-z-139.zip
Unzip it to a folder and click on the CPUz icon