I3 2120 Bogged by 7zip in new build or is it the HDD?

I just build my wife a new PC. Asus p8h67-m pro, I3 2120, 8gb ddr3 1600 (downclocked to 1333), gtx 570, and I am reusing her old WD Blue 320gb hdd.

I ran into a problem while Unzipping a file using 7zip though. I had a file unzipping at a laughable 20MBps tops (is this normal?) While opening control panel...then it happens. The whole thing just locks up for about 30 seconds. I have not had this happen in...well, a very long time on any PC in my house. Aside from being really frustrating, it makes me worry whether everything is going as smoothly as it should.

The hard drive test fine on my PC
A seperate non OS drive test fine on her new PC (so I know the sata are good)
So, is it really that easy to bog down an i3, and has anyone else had this problem before?

So my first ? is 1) Is it normal for 7zip to unzip a file that slowly with an I3...I mean it stays almost EXACTLY at 20Mbps from start to finish, which in itself makes me think there may be an issue. Even my i5 2500k 4.5ghz starts off amazing and then slows/evens out.

Is there something with the hard drive I could be over looking that could cause a file to cap at 20MBps unzip? I have gotten so used to using a SSD on my system that even normal drives feel slow to me...So, I am not sure if this is all just in my head or not.

Any help for an over tired husband who promised a new, more powerful, pink pc to his wife would be greatly appreciated.