If you can withstand 70 jin with ease, that means you can probably withstand 100 jin maximum. In that case, obviously 2 people hitting you with 50 jin each wouldn't break you.
I'm not saying the speed really doubles, but rather, that it produces a similar outcome as the doubling of speed (which is kicking your opponent's a$$ with ease).No.
Every movement is still occurring at the same speed as if there was only one guy there, there is just another thing to deal with.