Gosh, that is one of the things I really wanna do someday. I have been riding my bike which is about 125cc for about 10 years now but I could never take it to a speed where I could feel the adrenaline.
As you said 250cc is more than enough for a beginner to follow the dry uneven tracks and, I am astonished that you haven't tried a geared bike before but you could manage with a few falls only Lol
Geared bikes usually come with big engines and the need to then speed. Speeding in SEA especially where I am is a deathwish!