If you can go 40+ mph then you can take the lane in most places. I use a 4 stroke because reliability can be a huge issue with the 2 strokes from vibration. I have no problem running over 50 mph going downhill and 45 mph on the flats if no headwind.
Some good rim brakes can be just as strong as disk brakes, if the rear tire can slide and if the front brake can pick up the rear wheel on a hard stop then it has reached the maximum traction the tire can take and disks won't stop you faster. Better yet, think of the rim as a giant disk brake.