Having followed this discussion it prompted me to actually time my campaign load.
I was surprised.
Rig Tested:
P4 3.4Ghz
1GB Ram
Using the Merged Campaign, my save game/career loaded in 3min 47sec.
You could have knocked me down with a feather as it feels a lot longer than that when I'm sat waiting.
Anyway, there's probably only one major difference to my setup than most.
I locate my pagefile/swapfile on a HDD that is not used to run SH3/GWX. This means, that when SH3 uses up the physical memory/RAM while loading the campaign/game data, it starts to use a dedicated area of your HDD as virtual memory space. Now if this virtual memory is located on a different volume than SH3, is means that the data is only being read/written in one direction, i.e Read from SH3 & written to 2nd HDD only.
If the pagefile is located on the same volume as SH3, your HDD will need to read data, stop, write data, stop, read, stop, write etc..... This is over simplified but is the basics of what happens.
If you can/have a second HDD, I would suggest this method to aid in your loading times.