I've been riding with a few friends lately who all have 600s and 1000s and drive what they call "slow". Of course their idea of slow is 90+mph and I have to push the bike pretty hard to keep up with.
I feel like this puts a big strain on the engine and I'm wondering if I should be changing to synthetic oil, lubing the chain more often and etc.
Any suggestions from the more experienced out there?
Sure. Find other people to ride with, or go ride by yourself. That's how you survive to become more experienced yourself.
Synthetic oil is a big waste of money on the GS, IMHO - if you have any actual reason for concern (which you may not) change plain old dinosaur oil twice as often. It's cheaper and will do more good.
If you have an o-ring chain, and you are not riding in particularly dirty areas, no reason to step up the 600 mile cleaning - the bulk of the lube is inside the o-rings, and the exterior cleaning and lubing is comparatively minor. On the other hand, if you ride in dusty/dirty areas, you want to clean the chain much more often, and the air filter as well.