This is about fun, not performance. These are play bikes.
If you look at my Avatar, I am cruising around on a 50.
Ridges avatar was a near mishap on a CRF100F.
I can honestly say the CRF100F is pretty close to the most fun I have had on a motorycle. My experience on 2strokers is all bad. Painful crashes that have results in hitting so hard, I was left weezing on the ground. I wrecked on the four stroke plenty, but nothing too serious.
I have no intentions of moto-cross. However, some metro areas have 4 stroke 125 indoor racing. Slap a set of slicks on the bike, get leathered up and race on indoor go cart tracks!