I am looking into getting spare pads for my Shimano BR-RS785 brake calipers, what and I am wondering is what is the difference between the different pad compounds. I read a few articles online about it, but they seem to contradict each other

The two pads I was able to find online to replace my current ones are say
"Resin Brake Pad" and "Metal pad material"

https://www.bicyclesonline.com.au/sh...FQQHvAodwewAOA
wiggle.com.au | Shimano XTR BR-M985 Metal Pad With Cooling Fin | Disc Brake Pads

Different materials for different conditions and results. Some companies like EB also make organic pads, they cost a little more and wear faster but you typically get more "bite" with them. I'd see if your LBS can offer other options or check online (Jenson, Pricepoint.com and Cambria should have some)

3rd party companies like Kool Stop, also make sintered pads and Organic , plus offer steel or alloy backing plates

+ for extreme heat dissipation there are finned heat sink backing pads.

metallic sintered pads wear the disc more rapidly

It depends on your riding conditions and how you prefer your brakes to behave. Organic or resin pads are the default option and are smooth in application and medium in wear. Metallic pads are harder wearing and better for dirty/muddy conditions but have a less progressive feel. Sintered metal pads are rarer but are the best for extreme mud, think cyclocross.

Here:

Brake Pads - A break down of what you need to know - Pinkbike

So from that I think maybe organic pads would be best for me?

I'm 70kg, and will carry 6kg of gear when I tour, I plan to use the replacement pads in Japan in December, I use 160mm rotors, with hydrualic calipers.