EMC 2544 break down at iFixit is helpful.
I didn´t need to use any software to see the speeds because I both could download at much higher speeds from my 100MBit internet connection and copy data faster wirelessly to and from my Apple Time Capsule hard drive.
Recently I upgraded the CPU to a i7 3.1GHz 3770S, and that too was an easy job following iFixit guides. The iMac doesn´t like to be tampered with repeatedly but now there´s nothing more I can upgrade:)
Beware one cannot upgrade to just any CPU, it has to be one that has the same or lower thermal requirement from the heat sink.
Again, as some people have mentioned, this is all pretty bold warranty breaking stuff:)
Can I just add that the recovery system does not seem to have the correct driver for the WiFi card so if you plan on doing a internet recovery it will need to be via ethernet. I just carried the imac upstairs and connected it with cable and it was ok. The reason I needed recovery was because I sat the iMac up with two SSD drives in Raid0 and then managed to use up all the space. I was not able to get the imac going again until I reinstalled osx and restored from backup.