Doom,
That is a pretty good time - maintaining a pace of under 5min per km for 12km is impressive. You will find there are a great deal of Canadian Forces members out there who cannot even run 12km, never mind keeping up a strong pace like that. However, don't rest on your laurels, there will always be someone faster during unit and brigade harrier runs and sports days, so you'll want to keep your edge up!
I am assuming that this timing is for an unencumbered run. I'd suggest that whatever training regime you have been following for running has been working out well for you. It may be good to temper that with some weight-load work, running or shuffling carrying some weight. Running is good - it is one of the bases for overall fitness. However, being able to march long distances and carry a load is also important for many CF trades.
Don't kill yourself doing this - you will find that after your first encumbered session, your back and shoulders will ache in ways that you don't expect - no matter how much weight training, endurance or circuit training you do, the only thing that really accustoms the body to carrying a load for extended distances is to actually do it.
Set this as a goal:
http://www.army.forces.gc.ca/LF/English/6_1_1.asp?id=800 and remember the hardest part is crossing the start line.
Best of luck.