It's been awhile but I was very competitive with a rear motor B5 in the 17.5 class at my local, somewhat tight indoor med-high grip track. Modern motors and lipos are very light allowing a lot of latitude with weight distribution tuning. The modern mid motor cars are highly evolved and the much improved polar moment of inertia over a rear motor car can't be dismissed. Still, the difference was typically .2 to .5 per lap, depending of layout. Still collected tons of club level wins with clean, consistent, and smart driving. If they still ran 1/10 on our big, loose outdoor track, I wouldn't hesitate to break out my rear motor stuff.