The larger radiator you have to cool the water the more efficent the chargecooler will be. Water can hold many many times more heat than air. There is limited room for a intercooler on the RST so a chargecooler solution is more effecient since it doesn't need so much space. The chargecooler is efficent even with a small system. The radiator can also be fitted with a fan. Escort Cosworth had a chargecooler, so did the Lotus Esprit.

My plan is to convert the original intercooler to a chargecooler with some soldering or welding. A radiator (heater core size) and a pump is also needed.