Ronnydog, on the subject of jetting, as Qwerty says it is almost impossible to predict before you start to ride the new engine.
Here is a good example. I have converted two 125 engines, one to 200 high comp. and one to 225 standard comp.
Now in the 125 carb MV28mm TK same as 200, the 125 engine has a 134 main jet and a 34 pilot, this is actually too rich for a 225 engine and in the 200 high comp it's very lean.
It just seems wrong that a little 125 requires bigger jets than the 225, I think it must be to do with the swept volume that the shorter intake stroke sucks in less fuel.
But I'm only guessing.
Keihin 393 series mains fit the TK carb and are easier to find but the numbers don't cross reference so if you go this route you will need to find a base setting number first.
You are right, the 125 engine doesn't draw as much vacuum, and vacuum is what lifts fuel from the bowl. An engine rebuild with a radical cam won't hardly idle because of the lack of vacuum, no matter what jets are installed. On the other hand, a more efficient, higher output engine will also need bigger jets because more air is flowing through the engine at high rpm and WFO, because of the low vacuum conditions.
EDIT: When I get around to rebuilding Tdub, first order of business will be mildly porting the head, port matching, and a bigger carb, along with more cam and stiffer springs. I think with the stock cam and head, once jetting is right, other changes will move the powerband up and down the rpm range, but not really change the amount of thrust generated. I think cam and head work are the first effective steps to more power, with a bigger carb next in line, followed by freer flowing intake and exhaust. Only then will a bore and/or stroke be able to make significant power gains. XR100.com used to build TTR230 engines bored to 250cc to 28hp, and the first step in the process was headwork and cam. The potential is there, but I'd worry about durability and the narrowing effect on the powerband, especially with the TW trans ratios.