Try this then see if you still want to buy Challenger this is for all you cheapskates out there.
Take an old fly viper remove the ceramic magnet and fit 2 oblong neo mags ,stacked,as near to the rear axle line as possible ,you will need to cut the chassis to accept these.Tape the contoller in the full on position . Put the car on the track and it will probably go round flat out (it does on my track ,60ft polistil 3.8 secs, and also round a carerra oval)if it doesnt , add a couple of tweakers or another bar mag inside the chassis .Now try and race against it ,if you have unequal lanes put the mag car on the inside ,you will struggle to beat it .
Total cost 2-3 bar mags + 1 old fly viper
Ebeneezer Scrooge(keeping down the cost of Christmas)