Why 125? A 250 would mean you could overtake
the kawasaki ninja 250 is a great low capacity sport bike, Would be much safer if you wanted someone on the back as well
A great 125 sport bike is the aprillia. They have just brought out a 4 stroke i belive although most 125 four strokes lack any grunt and a hill can seriously slow you down. Stick to the 2 stroke de restricted ones, watch out they have not been used for racing though!
Anyway goodluck picking the right bike
Oh and the 2 strokes sound amazing