Tweeking suspension for luggage allowance

[Umarth]

Not sure if this is the proper place to ask this, but here goes:

I've got me a ktm 640 with a stock suspension setup.
I'm about to leave on a long trip and will have quite a bit of weight in luggage (starting with alu cases).

at 175, I'm right where the bike's suspension was designed for at the factory. But by adding 50-60lbs of junk on the rear end, that def. is busting the upper range. So I'm thinking that a bigger rear spring would be needed.

If it was just my weight that required stiffer springs, then both front and back need to be changed. My question is, if I go to a bigger rear spring because of the extra luggage (essentially extra weight over the rear wheel), do I also need to upgrade the front springs?

so, just the rear? of rear and front?

thanks