What type of riding do you do mate, as I reckon a well tuned smaller carb would be better then a larger carb.
What I mean is I suppose if you spend all your time WOT then yeah go for the 26 but you'll loose some down low grunt.
I'd prefer power down low and mid over top as I don't really get my bikes screaming their tits off.
My 140 loves the 24mm oko and feels strong all through the power, up against the exact same bike mine smokes it with a 30mm mikuni.
You'll get it mate, also don't worry about all this 2 turns out business on the mixture and setting stuff, it's good for reference but what ever works, works mate.
I'm only a half turn out on mine and it starts second kick every time and has perfect plug color.