NTC3 -
aluminium shocks
carbon woven diffs, topdeck, and shock towers
pan car style design
full adjustable camber
full adjustable caster
full adjustable toe in
adjustable width, ride hight, droop, and wheelbase
2.5mm 6061 chassis with burling
RS4 - has none of these features
Oh - and the NTC3 currently holds more national championship wins than any other touring car. Along with that - Team Associated has been building factory team race nitro race cars for over 25 years. Hpi has only won 1 national race, and it wasn't with the Rs4.
bottom line - want a professional race car? by the NTC3. Want a toy to bash with - get the hpi