hey Bo!
We're leaving for a RTW trip on a wee two up in August. It's like with every other thing - there's as many options as many people there are touring. I'm gonna tell you what we're taking for our trip.
Starting with the panniers:
We're taking Plastic GIVI Keyless panniers on the original GIVI tubular Rack. All that topped of with a GIVI Maxia topcase. I think that alltogether they provide abour 134L of baggage space.
Why plastic? Obviously after seeing other people we thought about going for aluminium panniers by Metal Mule or Touratech - problem is they're so bloody big there was no room for the wife in the back and also they're (in my opinion) overpiced. I think that putting them on and off the bike seems to be too much hastle: with Givi it's about 5 seconds - all you hear is "CLICK" , "CLICK" "CLICK" and they're on - you're ready to go.
OK they're plastic BUT let's say that we end up on the ground with the bike (I'm sure this will happen many many times on our trip). If you're carrying aluminium panniers they usualy end up out of shape - you must spend a lot of time putting them back to order - because it's not that easy to bend aluminium you will need a nice hammer and blacksmithing abilities

Here I would like to show one of my favourite films on youtube:
YouTube - Lovely Day in the Congo
If you see yourelf doing what Geoff is doing with every fall go for aluminium.
Ok with the plastic ones you might end up with them broken up - they won't loose their shape though - so all you need is duck tape them on both sides and you're sorted. 5 minutes job and you're on your way. That's my take on the subject and our life on the road will verify this statement, but I'm not worried...
When it comes to tyres we're going for anakee/ anakee2 kind of tyres - we're not in it for racing or big time offroading - WE WANT the tyres to last as long as possible and that's our main priority. I think tourance type tyres will last the longest when used both on tarmac and gravel.
We've been where you are and to be honest with you I slowely stop caring

I don't really care anymore what kind of tyres we're gonna take what is going to happen to the panniers etc. These are all "what if's" that don't really matter I think. People tend to get too focused on the GEAR factor. I wonder sometimes how did people manage these trips 30 years ago? Now you have ATMs in every larger town, you can get any part shipped to you in a matter of days sometimes weeks so at the end of the day the emergencies become just costly inconveniances...
Final thought: Take whatever you fancy and feel safe / good / comfortable with and GO FOR IT BUD!!!
Stay safe!
Andy