This all sounds pretty reasonable with your setup.
10 minute timeline exports in around 15 minutes, as you say. Now you export 4.5 hours, so that would be around 7 hours rendering time, add MRQ and multiply the 7 by a factor 3 and you end up with around 21 hours, add the CC and overlay and it all makes perfect sense.
Your major problem is your single hard disk drive. If you want to know if your system is properly equipped and setup, run the PPBM5 benchmark. http://ppbm5.com/index.html
As Harm said, only 1 hard drive is your problem... that is below minimum specifications
You need AT LEAST another 7200rpm hard driver (NEVER a partition!!!) for your video files
Trying to use only ONE Hard Drive for Video Editing
You are a music conductor, with a baton that you use to point to various parts of the orchestra... this is like Windows pointing to various parts of the hard drive to do Windows housekeeping or to load program segments for various functions
Now, at the same time and with the same hand... while still using the baton to conduct the orchestra... pick up a bow and play a fiddle... this would be doing something with your video file at the same time as all the other work
You as a person cannot do both at the same time with the same hand
A computer is a LITTLE better, in that it can switch from one kind of task to another very quickly... but not quickly enough for EASY video editing
You need AT LEAST two hard drives (separate drives, never a partition http://forums.adobe.com/thread/650708 for more) with Windows (or Mac OS) and software on your boot drive, and video files on a 2nd drive so the boot drive is not slowed down by trying to do everything
Partition = Crash http://forums.adobe.com/thread/957286
Ok, so a single hard drive is the problem.
OK, Ive been looking to get a SSD, I know they cost alot for a pretty small amount of storage compared with the standard hard drives.
So, if I do get another hard drive, would I need to move over all my adobe software to it so it all works from there, or just put the videos on it, so it can render the the video from the file which is saved on the SSD?
Boot drive for Windows and all software
Data drive for all video files
I use 3 drives
My 3 hard drives for video editing are configured as...
1 - 320Gig Boot for Win7 64bit Pro and ALL program installs
2 - 320Gig data for Win7 paging swap file and video project files
When I create a project on #2 drive, the various work files follow,
so my boot drive is not used for the media cache folders and files
3 - 1Terabyte data for all video files... input source & output export files (1)
(1) for faster input/output if you have 4 drives
- use drive 3 for all source files
- use drive 4 for all output files