I’ve toured on my pre disc mount version twice. Both times have been with a mini mugsy in a trailer, a tent and a 35l drybag bungeed across the top of the trailer, two rear panniers and a thermarest across the top of the rack.
It didn’t flex to the point of being unrideable and I put up with it.I can;t remember flex being an issue. Pinch punctures were a pain but that’s my fault for running the weight with 25mm tyres…..
However this summers tour was done similarly loaded on my singlespped rigid inbred with 1.5″ tyres. I know which one I’ll be riding for next years tour whilst the kaffenback has been stripped down and replaced with an Uncle John.
I will also say this, Mrs Mugsy on all these trips has taken her road rat. the 1st time (pre micro mugsy)she had 2 rear panniers. The 2nd time a child seat and micro mugsy whilst I had mini mugsy, and this year she had mini mugsy on a follow me tandem and front and rear panniers. She won’t be taking the roadrat next year. I’m supirsed she and the bike managed 10km from our start point…..
So the kaff is flexy, but I think less flexy than a roadrat, and I would concur that 4 panniers will probably cause more handling issues than 2 panniers even with same weight.
…..get a touring bike, or a rigid mtb for touring unless light weight touring.