Howdy.
Yamaha Motor Corp. doesn't import the XT125R into the USA, but the same engine design is sold here with the TT-R125LE.
I've owned five TT-R125Ls or LEs (still own one) and a WR250R and WR250X, and I can tell you that the WR250R will feel like a Superbike as far as power output goes.
It has twice the displacement, after all.
The down side is that it will be physically larger than your XT, but, most would agree it is the better choice for higher speed riding, both on or off-road, and with your height, it should be a good fit.
What are you waiting for? :)